Magus (person)

The Magus is Adam Warlock's future self, in a timeline where he has turned out to be quite the villain. He got to be this way because the Magus would come back from the future, beat up his younger self, then give him to the In-Betweener to be worked over for centuries by Lord Chaos and Master Order until it was inevitable that he become the Magus. (Aren't time loops fun?) He has all the powers of Adam Warlock, as well as his soul gem.

Adam Warlock is the chosen champion of life. This applies to the Magus, even though he would commit genocide using his Universal Church of Truth. Eventually, the Magus had taken over all of the universe that he had come into contact with. Death did not like what was going on with Life's champion, so she sent her champion Thanos to stop the Magus' plans. Thanos helped Adam Warlock erase the Magus' timeline from existence, so Death would triumph over Life.

So the Magus had never existed...until Adam Warlock got a hold of the Infinity Gauntlet and effectively became God. To ensure infallibility, he expelled all good and evil from himself. The evil side became the Magus. This time, the Magus was just a shade of Adam Warlock, but he was extremely crafty. Through a series of manipulations, the Magus gained the Infinity Gauntlet. (This was in The Infinity War.) However, the reality gem was a fake, and so ultimate power was not his. He was promptly absorbed into the soul gem. A power-stealing villain named Siphonn (or some such thing) stole the soul gem from Warlock for a brief period of time. Because Siphonn did not have the same degree of control over the gem as Warlock did, the Magus was able to escape before Warlock reclaimed the gem. Lately, the Magus has been harassing the new Captain Marvel, using new power-stealing abilities he picked up from Siphonn.