The Order of Ixis was an ancient society of sorcerers that originated many centuries before the birth of Sonic the Hedgehog, roughly 9,700 years ago.
Founded by Ixis Mogul, who developed much of the Order's knowledge as he gained increased understanding of his Chaos abilities, the Order soon drew other beings who were interested in obtaining power through the natural forces on Mobius. Eventually, this group became involved in a war with the Albion Knights of Aurora known as the Forgotten War, which ended with the Order's defeat and destruction. (StH: #163)
After Operation: Clean Sweep created by Doctor Eggman, the spirits of the Ixis sorcerers were re-awakened in Ixis Naugus' body, haunting him of the past and each desiring to control Naugus' body as their own. They cannot be seen or heard by other beings, and will often create thoughts in Naugus' head as if he had a few split personalities. Eventually, this led to a new Ixis Resurgence. (StH: #225, #226, #227, #228, #229, #231, SU: #35)