The Dragon Ring belongs to the Dragon Master. The first of this title was Hotep-Ra but he was not likely the creator. The second and current holder of the title and ring is Septimus Heap. It glows when someone of significant Magykal power puts it on and even if the Ring is too big on the finger of the wearer, it will curve and tighten itself until it fit on his or her finger. It is also able to restore any Magykal energy you have lost but does not increase any Magyk the weilder has lost. It is lost after many years by Hotep Ra and is later found when Septimus Heap (at the time Boy 412) finds it in the secret tunnels of Aunt Zelda's cupboard on the cottage withing Daggen Island in the Mirram Marshes. It glows and identifies Septimus as the new Dragon Master. It is breifly left to Marcia while she's held captive aboard DomDaniel's boat but later returned to Septimus. This all happens in book 1, Magyk.
In Aunt Zelda's History of the Dragon Rings, it is shown that the Dragon Ring has a twin dragon ring, but rather its Twin is the Skye Ring. It is said to be held by the Anas deep within the Forest, deeper even than the Forest Way.