Osiris

"Oryx-Dead-King. Oryx-Dead-King. Three words, nine-word bursts over and over. Osiris?"

- Master Rahool

Osiris was an old Warlock who was exiled from The City. He had knowledge about the inner working of the Hive, as he knew about the Shrine of Oryx. He was also said to have "come too close" to understanding the Vex.

Trivia
Before the release of the game, it was thought that Osiris was one of several factions in The City.