Magus is a villain of the Marvel universe and is primarily an enemy of the X-Men. He is the patriarch of an alien species known as the Technarchy - a living, sentient, techno-organic virus Magus and his kin exist to conquer and annex entire worlds yet he has a wayward son in the form of Warlock, who has allied with the X-Men against him: the two characters share names with unrelated Marvel characters (Magus and Adam Warlock respectively).
Magus was the ruler of his native world, and, apparently, its most powerful being. When his son Warlock fled, because he was afraid of having to face his father in combat, Magus pursued him to Earth in order to kill him.
The mutant-haters, the Purifiers, discovered Magus in a hibernation state on the ocean floor. Bastion collected Magus and used the transmode virus to resuscitate and transform long-dead enemies of the X-Men into the members of the Human Council.
Eli Bard stole the techno-organic virus from Magus, apparently killing him.