Marcellus Pye was the last Alchemist and a renowned Physician who lived in the castle five hundred years in the past. He had discovered a Tincture that grants eternal life but not eternal youth, causing him still be alive while decaying and being horribly sick in Septimus Heap's time.
Marcellus Pye was born to Queen Etheldredda and her consort at least 500 years before the events of Magyk.  Marcellus is Etheldredda's oldest child and her only son. He had 3 younger sisters, Esmeralda, who would become Queen in her own right, and his infant twin sisters, who are implied to have been killed by their mother and the vicious Bumptious Barrelle of Larde. Much of his early life is unknown, but it appears he had a natural gift for Alchemie and Physik. He also made fast friends with Julius Pike, who would become ExtraOrdinary Wizard. 
A Promising Young Alchemist
As a young man, Marcellus was obsessed over the main secrets of Alchemie: gold, eternal life, and Glasses of Time. Learning about Glasses from a young age, Marcellus found the formula to make a Glass of Time in the Manuscriptorium, memorized and then burned it. However, his initial experiments didn't work and only travelled through solid walls. Marcellus gave one of these Glasses to his mother and the other to the then-Chief Hermetic Scribe, who didn't realize that Marcellus was using it to get into the Hermetic Chamber. The Alchemist then decided to try fusing Glasses together--and came up with the Glass of Time he sought. However, after sending many scribes and eventually his best friend through the Glass with no return, he decided to Lock the doors to the Glass of Time. Marcellus decided to return to the earlier transportation Glasses, for he wished to learn from the Darke Alchemists in the Land of the Long Nights. Unfortunately, the captain he hired to transport the Glass double-crossed him and sold it to the merchant Drago Mills, whose warehouse was impounded and eventually became the home of Alice Nettles. The other Glass from this pair was put into a cupboard, as it was apparently useless, and then made its way to the Palace. Following his unsuccessful ventures with Glasses, Marcellus decided to stick with gold. Sometime during his rise to power, he married the Keeper Broda. While Marcellus and Broda had a happy marriage, it was known that Marcellus would use Broda's access to get into places he would not normally be able to go, like the Queen's Way. His travels left pockets of Darkenesse hanging around the Way. Marcellus also once apparently possessed the Flyte Charm, but lost it somehow over the years. 
Meeting Septimus Heap
Marcellus had begun making a Tincture for Eternal Life. While the recipe succeeded, it did not stop Marcellus aging, meaning that 500 years of Castle history passed over his head while he grew feeble, old and disgusting, unable to care for himself. However, when Silas Heap UnSealed the portrait of Etheldredda in the Palace and unknowingly freed Marcellus' wicked mother, he struck a deal with her to lure Septimus Heap, who had the powers of the seventh son of a seventh son, into his grasp so he could fix the formula for them both in the past. 
Etheldredda coerced Septimus into looking into a glass in the Queen's Room through the use of a Reclaime. Unknown to Septimus and Jenna, this was the Looking Glass that Marcellus had given Etheldredda, and the aged Marcellus was able to seize Septimus despite the best efforts of the Princess. Septimus attempted to escape the Alchemist with the Flyte Charm, but Marcellus was able to get it back from him and eventually send Septimus into the past--though not before his handsome past self got a look at what he would become. 
The Seventh of the Seventh and the Alchemist
After bringing Septimus to the past, Marcellus attempted to get the boy settled in, giving him his own personal Physik chest--although it could only be opened with Marcellus' Keye. Septimus, longing to return home and unable to effectively communicate with the past denizens of the Castle, did not speak, except for one instance when he described Marcellus' future appearance in great detail, much to the Alchemist's discomfort. On Loki's Day following the equinox, Marcellus, Septimus, and his scribes sealed his great work: the I, Marcellus. Following the sealing, Marcellus learns from Septimus that the Tincture can only be completed in 2 days. The Alchemist, noting the poor state of his Apprentice, decides to shoo him out for the Winter Faire. 
Marcellus is then summoned for Etheldredda's banquet commemorating his younger sister Esmeralda's return (though in truth it is actually Jenna, who is nearly identical to the vanished princess). Etheldredda occupies much of Marcellus' attention at the table and thus he is unable to talk to Jenna (whom he also believes is Esmeralda). The banquet comes to a head when Hugo Tenderfoot spills boiling sauce on the Queen, triggering an all-out melee involving Septimus (who snuck into the Palace in disguise), Jenna, Hugo, the Bumptious Barrelle, Etheldredda, and Marcellus. Septimus and his companions attempt to flee to the Great Chamber of Alchemie and Physik and ambush Marcellus for the Keye, but Etheldredda's Aie-Aie foils the plan by screaming and drawing the Spirit-Seer Transformer Ullr out of hiding. Etheldredda and the Aie-Aie drink the incomplete Tincture and the mad Queen attempts to murder Jenna, although she drowns in the river outside. Marcellus, who hid in a closet during the chaos, is momentarily shocked at his mother's death but overcomes it. As the conjunction of 13 planets that he needs to remake the Tincture is passed, Septimus realizes that the conjunction is happening again in his original Time. Septimus, Jenna, and Ullr pass through the Glass of Time (getting separated from Snorri and Nicko in the process) and Septimus makes the Tincture for the aged present-day Marcellus, causing him to become young again. Marcellus rewards Septimus with the Flyte Charm and his Physik Chest, complete with an antidote for the Sickenesse. The past Marcellus helps Julius Pike capture and kill the Aie-Aie and seal both the creature and Etheldredda--now a Substantial Spirit--into the painting that Silas Heap would later UnSeal. Marcellus also decides to take on Hugo Tenderfoot as a Physik apprentice, and the boy becomes a very good Physician in his own right. When Nicko and Snorri return to Marcellus, having missed the window of opportunity to enter the Glass of Time, Marcellus helps them plan for a return to their own time through the House of Foryx. 
Later Life and the Great Alchemie Disaster
When Esmeralda, who stood to inherit the throne after Etheldredda, found out about her mother's death, she had a nervous breakdown and instead lived with Broda for a time. Marcellus served as Regent while also conducting his Alchemie experiments. Marcellus cedes the throne to Esmeralda when the Time Is Right for her to rule. 
As was custom for that time, Marcellus was invited to the Draw for the Queste for Julius' dear Apprentice Syrah Syara. He witnessed Syrah attempt to punch the ghost of Tertius Fume in the face, and like Julius and everyone else, assumed Syrah died. It is unknown whether Marcellus ever learned of Syrah's survival to the present day. 
At some point, Marcellus and Julius found the Darke Two-Faced Ring. Marcellus decided to DeNature it in the Great Chamber of Fyre. However, Julius interfered, causing the Fyre to spread out of control. Julius then forced Marcellus out of the Chamber, leaving his Drummin creations to die, and iced over the tunnels beneath the Castle. Julius then decreed that every ExtraOrdinary Wizard from then on would swear to abhor anything Alchemical. The event would be known as The Great Alchemie Disaster. Unknown to Julius and Marcellus, the Drummins, the Chamber and the Ring all survived, and the Ring would eventually find its way to the Necromancer DomDaniel.  A grief-stricken Marcellus seals the Chamber of Alchemie and the Chamber of Fyre with his Keye and submits to Julius' elimination of the Chamber from history.
Return to Castle life in the Present Day
Septimus, correctly fearing the reaction of Marcia to a healthy Marcellus, keeps his visits low-key, seeing the Alchemist under the pretense of seeing his mother Sarah. To ease the shock of the modern day Castle on Marcellus, Septimus has a pair of shoes made in the old fashion that Marcellus likes. Unfortunately, Marcia discovers these and the existence of the Alchemist. Marcellus has inhabited his house on Snake Slipway, above where his old Chamber of Alchemie and Physik was situated, and meets Beetle for the first time (and gets into the habit of calling him Scribe Beetle, although Beetle has never been a scribe at the Manuscriptorium). Marcellus shows Jenna, Beetle, and Septimus Nicko and Snorri's notes from 500 years ago and details what he has heard about their journey after they left him. However, Marcia sniffs out his house and confronts the old Alchemist, although Marcellus is quite polite as the ExtraOrdinary Wizard takes her Apprentice back to the tower. 
Marcellus is not seen for quite some time, until Septimus is coerced into the Queste. A desperate Marcia Overstrand summons the Alchemist to the Wizard Tower where Marcellus informs her of what has happened to her Apprentice. The two attempt to gain access to the Manuscriptorium Vaults, but Chief Hermetic Scribe Jillie Djinn bans them, allegedly because her scribes are occupied but in reality due to her suspicion of Marcellus and Alchemie. 
Marcellus does not make a direct appearance during the events of Syren. However, both Septimus and Syrah make use of his Physik to begin healing Spit Fyre. Syrah also tells Septimus of how Marcellus refused to tell Julius what happened to the strange Apprentice, driving a rift between the two old friends. 
The Darke Domaine
Marcellus is invited to the Wizard Tower to help Marcia and Septimus decide when the time is right for Septimus to enter the Darke Halls for his Darke Week. However, neither Septimus nor Marcia tell Marcellus that the other reason for Septimus to enter the Darke Halls perfectly is so that Septimus can save the ghost of Alther Mella, who was accidentally Banished there. Marcellus recommends the Darke of the Moon, which displeases Marcia and ends up displeasing Marcellus in turn. The Alchemist tells his Apprentice to meet him at his house later for another weapon against the Darke. Marcellus explains the dangers of the Darke to Septimus (inadvertently causing him to miss leading his Call Out in the process). Marcellus helps him create a Darke name, Sum, and gives him a Darke Disguise and a Darke rope to protect himself in the Darke Halls. After dismissing Septimus, Marcellus goes to the Palace for Jenna's birthday party, but sees the freed Darke Domaine escape the SafetyCurtain. He, Beetle, and Marcia capture Merrin Meredith in the Manuscriptorium, and Beetle volunteers to be sealed into the Hermetic Chamber. However, Merrin, empowered by the Darke Domaine, breaks through all of Marcia's spells, and before the ExtraOrdinary Wizard can rashly pursue the mad Darke Wizard Marcellus is forced to stop her. As Marcia goes to activate the Wizard Tower SafeShields, Marcellus decides to head through the Castle Canyons to find his Apprentice. Marcellus finds Septimus after the Apprentice comes to leave Jenna at the Alchemist's SafeChamber. Marcellus disagrees with Septimus' plan, realizing that Jillie Djinn, as Chief Hermetic Scribe, has revealed the SafeChamber's existence and it is not so safe. The Alchemist suggests the Ramblings , looking for a "an overlooked little fleapit down a dead end, with an outside window." Jenna decides to take them to the Heaps' old apartment, which satisfies all the requirements. The Alchemist and company encounter Simon Heap, Thunder, Lucy Gringe, Stanley and Sarah Heap. Marcellus stops Septimus from fighting his older brother, and takes command of the group as they travel through the Darke Domaine to the Ramblings. When the group reaches the Heap apartment, Marcellus witnesses Sarah stop yet another argument between Septimus and Simon, this time over an Anti-Darke. The following day, Marcellus himself intervenes between Septimus and Simon once again, and this time convinces his Apprentice that the reformed Simon can offer useful knowledge against the Darke. The Alchemist, meanwhile, performs the first set of calculations that will tell Septimus where the nearest Portal to the Darke Halls is. When the time comes to escape, Marcellus and Sarah Heap break from the established order and Marcellus leaves last. When Septimus confronts his master about his recklessness, Marcellus replies that "things that are right in the cold light of reason may feel very wrong in reality." Nicko rescues the stranded party from the Moat and Marcellus and Simon perform the final calculations for the Portal while Septimus sleeps. To his immense dismay, the Portal is in the Bottomless Whirlpool at Bleak Creek. After sending Septimus into the Darke Halls--which causes Marcellus immense stress--he witnesses his Apprentice and Spit Fyre battle Merrin and the Darke dragon over the Castle. Marcellus witnesses the Darke dragon fall and holds Merrin in custody. It is implied that he is the one who removes the Two-Faced Ring from Merrin, the Other way. Marcellus delivers the Two-Faced Ring into Marcia's custody, and asks the ExtraOrdinary Wizard if he can open up the Great Chamber of Fyre (with Septimus' assistance) and Marcia agrees. She then borrows six guineas from the Alchemist to pay an advance for Merrin's residence at the Doll House in the Port with his biological mother. It is later revealed that Marcellus' Darke Disguise that he gave to Septimus caused Marcia to dock a point off of his Darke Week examination. However, Septimus still earns a perfect score anyways thanks to his 8 out 7 mark on his capability to use the Darke in a balanced and responsible manner. 
DeNaturing the Two-Faced Ring
Marcellus is placed in charge of preparing the Chamber of Fyre to DeNature the Two-Faced Ring. However, Marcellus believes that Marcia will not stand for the old Great Chamber of Fyre, which is believed to have caused the Great Alchemie Disaster, to be re-opened. Marcellus leads Marcia to believe that the Fyre he will destroy the Ring with is a small furnace in the Chamber of Alchemie, and when he ignites the real Fyre, he must open it through various vents so as not to draw suspicion, and so that he can preserve the Ice Tunnels as per his agreement with Marcia. He is not entirely successful, however, as Beetle, with the aid of Romilly Badger, discovers a map of the vents with markings made by Marcellus 500 years ago.
Marcellus is nearly forced to reveal his deception early when he, Septimus, and Marcia discover that the decoy Chamber Marcellus planned to set up is filled with glass. However, they soon realize that only the outer portion of the Chamber is filled and the rest is sand, which can easily be siphoned out. Not yet ready to trust Septimus, who is to spend a month with Marcellus helping him work, Marcellus has him siphon the sand out. As the real Fyre's heat grows, Marcellus is forced to open four more vents.
Marcellus' movements have not gone undiscovered, as Beetle and the Manuscriptorium scribes have noted the positions of puddles and cross-referenced them against the old map that was written by Marcellus. Convinced that the Alchemist is up to something, Marcia and Beetle invite him to the top of the Wizard Tower for a confrontation. Marcellus manages to escape Marcia and Beetle's investigation by claiming the heat is from Spit Fyre's dragon blood, as spilled dragon's blood apparently never loses its heat. Neither the ExtraOrdinary Wizard nor the Chief Hermetic Scribe believe his ruse.
Jenna attempts to revive the Dragon Boat with the Tx3 Revive given to her by none other than Broda Pye, Marcellus' wife in the past. However, when she discovers that the third of the necessary bowls is eaten by the Marsh Python, she goes to Marcellus for help. Marcellus, reminding Jenna and Septimus that he too is of royal blood, and goes with them to Jannit Maarten's boatyard to help revive the Dragon Boat. Remembering when he, Esmeralda and Broda revived the boat themselves, he instructs Jenna to enter the boat's heart chamber and rub the Tx3 Revive on the dragon heart itself. He then advises Jenna to seek Marcia's counsel on what to do with the Dragon Boat, despite his own irritation with her.
Septimus informs Marcellus that he will not be returning to the Great Chamber of Alchemie, and Marcellus accepts gently, knowing that his own squabble with Marcia has contributed to this. Marcellus informs Septimus that he is being replaced, though Septimus does not know at the time that his replacement will be Simon Heap. After Septimus leaves, Marcellus visits Simon and Lucy, still moving into their new home, and gives Simon a copy of I, Marcellus, with instructions to read it and meet him to become the new Alchemie Apprentice.
Marcellus decides to entrust Septimus with knowledge of the Fyre, knowing that it is Septimus' last day before he returns to the Wizard Tower. Marcellus strictly instructs Septimus not to tell Marcia about the Fyre, although Septimus suspects that Marcia doesn't actually know about the great Alchemical Fyre beneath the Castle. Taking Septimus down in a moving chamber, Marcellus does not realize that he failed to maintain the chamber, and he and Septimus end up trapped. This also leads to Marcellus failing to keep his appointment with Simon. Eventually (thanks to an unintentional hail of bricks from Marcia) they get to the bottom. Marcellus makes one last offer to Septimus, but the boy once again turns down the Alchemie Apprenticeship, though he does ask if he can freely return to see the Fyre.
After finding out that both Marcia and Septimus are alright, Marcellus keeps his appointment with Simon and confirms that he wants him as his Apprentice. At Simon's official Alchemie Apprentice supper, Lucy gives Marcellus some prudent building advice (most Alchemists struggled to find builders) and Marcellus decides to put her in charge of building the chimney on Alchemie Way.
Once Lucy builds the chimney, Marcellus shows Simon and a visiting Septimus how he will bring the Fyre to full power. He lights the decoy fire in the Great Chamber of Alchemie, and returns to the surface, only to be confronted by angry Castle dwellers believing he will cause another Disaster. Marcellus then settles the matter with the offer of guided tours of the Great Chamber of Alchemie, run by Simon.
Marcellus goes with Simon to collect the Two-Faced Ring (he had offered Lucy the chance to go with them as payment for building the Alchemie Chimney, but she refused), but master and apprentice are turned away by Marcia, who does not want either of them to know that the Two-Faced Ring has been stolen by Edmund and Ernold Heap. Marcellus manages to deduce the Ring's theft anyways, and in doing so convinces an eavesdropping Alther that he did not steal it himself. Alther convinces Marcia to summon Marcellus and Simon back to the Tower.
Marcellus, Simon, Septimus and Marcia, joined by Beetle and Alther, hold a crisis meeting in the Pyramid Library. Marcellus, Simon and Beetle hear the full account of the Ring's theft by Edmund and Ernold, whom Simon deduces have been InHabited by the ring's previous tenants, the incredibly Darke Wizards Shamandrigger Saarn and Dramindonnor Naarn, after the Ring itself Migrates and returns to its original state.
Marcellus concludes that the gold that the Wizards must be sealed back into does not have to be in the gold band that they were in originally (that made the Two-Faced Ring). Septimus recalls the bowls for the Transubtiate Triple (which are useless as one has been eaten) were made from the same gold as the Two-Faced Ring and Jenna's royal circlet. Marcia decides to use Merrin Meredith, the Ring's former possessor, as bait.
When the Ring Wizards come to the Castle, having freed themselves from Edmund and Ernold, they smell the Fyre and decide to destroy it to prevent themselves from being destroyed. Marcellus is in the Chamber of Fyre, inspecting the Cauldron for weaknesses, when the Ring Wizards appear. In despair, he finds Duglius Drummin, whom he thought dead from the Great Alchemie Disaster. After meeting the Drummins, Marcellus sees the Ring Wizards Accelerating the Alchemical Fyre, intending to cause another catastrophe. After seeing Simon nearly get caught by the Wizards as he attempts to enter the Chamber, Marcellus realizes he will not be able to slow the Fyre, so he assigns that task to the Drummins while leaving to get help himself. The Drummins are successful in dousing the Fyre with coal (unlike normal fire, Alchemical Fyre is soothed by burning coal). However, this causes panic in the Castle, as fire bursts through the vents.
Marcellus climbs through the Drummin burrow and blacks out. When he comes to, he realizes not only what he has to do but also his anger at Julius Pike for attempting to destroy Alchemie within the Castle. He makes it out of the burrow into an Ice Tunnel, where he is nearly run down by the Purple Tube coming from the House of Foryx. The tube's drivers, Jenna and Septimus, take a very battered Marcellus to the Wizard Tower. However, the heat of the Fyre melts the Ice Tunnels, and Marcellus, Jenna, and Septimus nearly drown before Marcia is convinced that they are outside the Tower and lets them in.
While Septimus gets the final Committal, Marcellus sees the ghost of Julius Pike and aggressively confronts him about his role in the Great Alchemie Disaster. While Marcia is at first shocked at Marcellus' aggressive tone, she hears the full story of how Julius' casual disposal of the Two-Faced Ring damaged the Cauldron and how he refused to let Marcellus overcome the Fyre on his own. Julius apologizes to Marcellus, who tells him that his apology is better spared for the Drummins (he eventually apologizes to them after learning their ways).
Marcellus takes the Covert Way down along with Milo, Marcia, Septimus, Beetle, Jenna, Julius, and Syrah (who is the only person who can operate the Covert Way) and Rose. After Jenna successfully Commits the Ring Wizards back into the Two-Faced Ring, Marcellus DeNatures the Ring into lead. He repairs in full his relationship with Marcia and Magyk in general, to the point where he is invited to Marcia's rooms in the Wizard Tower to talk about Magyk and Alchemie with Hotep-Ra himself. The DeNatured ring is transmuted back into gold, the way it was when Hotep-Ra first gave it to the Queen long ago, and presented to Jenna for her Coronation by Marcia. Marcellus also makes the clasp and corners that adorn the rebound The Queen Rules that Hotep-Ra gives to Jenna--the first gold items to come out of the Great Chamber of Fyre since it was shut down all those years ago.
Marcellus Pye is described as a little vain, but overall a good person. He is a good older brother to his sister Esmeralda, attempting to shield her from her mother's evil and even ruling in her stead. He is a good master to both Septimus and Simon, and believes in giving people a second chance, as he showed when he accepted Simon as his newest Apprentice. Although he is closer to the Darke than most Wizards dare to get, Marcellus is staunchly against the misuse of Darke Magyk and instead uses it to protect those that he cares about.
Marcellus' vanity is displayed in his appearance and furnishings. His obsession with gold is well-known, with Marcellus littering the Great Chamber of Alchemie and Physik with gold objects and still having enough left over to create a decoy Chamber to deter thieves. Marcellus even wears gold in his clothes for special occasions and has a wide assortment of gold jewelry. Even outside of his love for gold, Marcellus wears fine clothes at all times, especially ostentatious shoes, and has been described as having a flair for the dramatic. When in the middle of a project, Marcellus is often unconcerned with the needs of other people, such as during the binding of his book when his scribes went hungry.
Marcellus is generally passive and prefers to avoid a fight rather than start one. However, when he knows he is right the Alchemist is quite stubborn, as demonstrated by his confrontations with Marcia Overstrand and Julius Pike.
Marcellus is known for being sneaky and deceptive when he needs to be, practicing those skills over a period of time. Many of his plans and experiments are kept away from all but a few trusted workers and apprentices such as Septimus Heap. Marcellus is not above lying to protect himself when need be, such as when Marcia and Beetle confronted him with the heat vents of the Great Chamber of Fyre and he deflected the blame onto Spit Fyre's dragon blood. The Alchemist is a smooth talker as well and capable of soothing over discord.
Marcellus has a disdain for most Wizards, partially due to regarding the Wizard Tower as a haven of gossip (which also explains his desire for secrecy) and due to his one-time best friend Julius Pike's role in destroying his life work. Marcellus also disagrees with many Wizarding methods, describing Wizards as chickens, pecking at the surface of things they cannot understand, particularly the Darke. While Marcellus respects Marcia and can work with her in a crisis, the two disagree vehemently on Septimus' status as their Apprentice. Marcellus is fine with working with Wizards prepared to follow his instructions, such as Simon and Septimus. Like Jenna and Beetle, Marcellus is uncomfortable in the presence of powerful Magyk, even that performed by his friends.
As Jenna's closest living relative on the royal side, Marcellus views her as another younger sister, explaining many facets of Queenly life to her that her late mother Cerys was unable to. Marcellus had a good relationship with the royal family in general, with the exception of his wicked mother.
In crises, Marcellus shows a tough and commanding side. The Alchemist is quick to stamp out dissent and to reach a course of action. He does not intend to leave people behind if he can help it and has a good gift for strategy. All of Marcellus' crisis management was displayed when he led Septimus, Simon, Sarah, Jenna, Lucy, Stanley and Thunder across the Darke Domaine and to the Portal. Marcellus is quite capable of working with people he would normally argue with, most notably Marcia Overstrand, during a crisis.
Like all Alchemists, Marcellus is legendarily stingy. His personal dwelling on Snake Slipway is poorly furnished (although this may be as much a protection for his Darke substances as for personal taste) and he was very reluctant to part with six guineas, even to reunite Merrin with his mother. Marcellus also tried to pay Lucy for her construction services with a visit to the Wizard Tower, and didn't understand why she stomped off furiously.
Despite appearing to be a young man, Marcellus is over 500 years old, and the stubbornness and forgetfulness of age can betray him. He failed to maintain the moving chamber to the Great Chamber of Fyre, nearly endangering Marcia and Septimus in the process, and often lapses into calling people by slightly inaccurate names, such as referring to Jenna as Esmeralda and Beetle (then an Inspection Clerk, and never a Manuscriptorium scribe prior to becoming the CHS) "Scribe Beetle," although he gets better with time.
Marcellus has a fear of both normal fire and the dark, and keeps his house on Snake Slipway constantly lit with candles, along with a well-placed bucket of water. He is quite uncomfortable with sunlight and society after all his years in the Old Way under the Castle, and has a little trouble adapting to the changes the Castle made in his absence (such as shoe system measurements, according to Terry Tarsal).
Powers, Abilities, and Possessions
- Eternal Life: Although the perfect eternal life is not Marcellus' own discovery--the formula is perfected by Septimus, and Hotep-Ra has achieved a technical immortality far before with his House of Foryx--Marcellus is the only known Alchemist to have created a successful tincture to grant eternal life. With the aid of Septimus, Marcellus retains his youth as well as his knowledge for over 500 years. While he is still prone to injuries, Time Slips and potentially even memory loss, the perfected Tincture will keep him from dying of natural causes eternally.
- Gold-making: Marcellus is particularly proficient at transmuting lead into gold, and his Chamber of Alchemie and Physik is littered with gold objects. Marcellus can also reverse gold into lead and can work with Magykal gold as well as ordinary gold, although he cannot create it.
- Alchemical Fyre: With the aid of his Great Chamber of Fyre, Marcellus can cultivate an Alchemical Fyre strong enough to DeNature the Two-Faced Ring while also heating the entire Castle during the Big Freezes. Marcellus also creates Fyre globes, which respond to touch and help him keep warm when he lives as an aged hermit in the Old Way. These Fyre Globes are also seen in a portable size that can be clipped onto a belt for Cauldron Inspections.
Aside from these main tenets of Alchemie, Marcellus was also skilled at making Glasses. He only ever made one True Glass of Time, but made a series of smaller Glasses that could transport people or objects over great distances. Marcellus is also the creator of the race of Drummins, a sentient race designed to inspect the Fyre. Marcellus also claims to know about the alchemical properties of dragon's blood
While Marcellus is best known for his Alchemical prowess, he was also a skilled Physician. He quickly creates an antidote to the Aie-Aie's Sickenesse. Marcellus is also known to have studied both the anatomy of vertebrate creatures, including dragons, and the combination of Magyk and Physik, both of which Septimus and Syrah call on to heal the injured Spit Fyre. Marcellus trains the young Hugo Tenderfoot and Septimus in Physik and both become skilled Physicians in their own right.
Darke and Magykal Knowledge
While Marcellus has no Magykal power, and distrusts Wizards in general, he has a better understanding of Magyk and the Darke than most non-Wizards and even a few Wizards. Marcellus possesses many Darke devices, such as the Darke Disguise he gives Septimus and his own cloak, which can repel the Darke to a degree, while also maintaining a SafeChamber in his house on Snake Slipway. Marcellus is responsible for the pockets of Darkenesse in the Queen's Way, due to his use of the passage while the Keeper was his wife. He learned some Darke Alchemical secrets from the Alchemists in the Land of the Long Nights. Marcellus was seen using a Darke Curse in the Darke Domaine to sweep a Thing away from his cloak, so it is likely he knows a few Reverse Incantations of his own.
It is implied that Marcellus has visited the Darke Halls before, for his description of them matches Septimus' own experience right down to the details. Marcellus is also able to calculate the location of a Portal to the Darke Halls with great accuracy, and knows the answers to the questions the beings within the Halls will ask a newcomer. His Darke Name is never mentioned in the series, but following the pattern of Septimus and the Ring Wizards, it would be Sul. Despite all his knowledge of the Darke, Marcellus does not consider himself a serious practitioner as Simon Heap once did, and does not seek to use the Darke to harm others.
Outside of the knowledge pertaining to his fields of study, Marcellus has some experience in governance, as he serves as Regent for Esmeralda until the Time Is Right. He also provides a wealth of royal advice that his closest living relative Jenna finds very handy. He is a sound mathematician, creating an entire section in his I, Marcellus for alchemical predictions that can be used to predict an Apprentice's Darke Week. Marcellus is a skilled architect and designer, designing the Great Chamber of Alchemie and Physik and a decoy Chamber to deter thieves as well as the Great Chamber of Fyre. His actual construction skills are quite poor, however. Septimus notes that the walls of his SafeChamber do not stay up straight all the way and the mortar for his Alchemie Chimney is soft and collapses easily. Marcellus' physical prowess is never highlighted in the series. Septimus thinks that he cannot outmatch Marcellus for the Keye with an ambush due to his size, but Nicko Heap manages to overpower him alone from behind.
"Marcellus" is a male given name that originates from "Mars," the Roman god of war. The name was commonly used in Rome and the Byzantine Empire among politicians, generals, and a saint. "Pye" may be a corruption of pi, the mathematical constant. This reflects Marcellus' logical, mathematical nature, and his immortality, as pi is a constant.