Ouroboros

Ouroboros is a type of Demon pursued by the Illuminati.

Overview
Ouroboros appear as stout, reptile-like demons with their tails held in their mouth.

They are amongst a number of high end demons considered difficult for Demon Eaters to possess, and those that can take control of such a demon are amongst the Illuminati's Chosen Ones.

Powers and Abilities
Ouroboros possess incredible regenerative properties, allowing for nearly unlimited cellular regeneration.

Trivia

 * The Ouroboros is an ancient Egyptian symbol of a serpent eating its own tail. It was later adopted by various mythologies and belief systems, most notably Alchemy.