The fact that Onslaught was responsible for Marvel's failed attempt to reboot the Marvel Universe in the '90s has led to him being somewhat reviled by many fans, but he's still a great villain who has a lot of potential to make a great big screen baddie somewhere down the line. He is in fact so powerful that The Avengers, Fantastic Four, and X-Men actually had to sacrifice themselves to stop him when he was first introduced. Made up of the consciousness of both Professor X and Magneto, Onslaught is essentially the psychic embodiment of the very worst of them both. He most recently made his presence felt when a new version was created thanks to the Red Skull grafting parts of the deceased Charles Xavier's mind into his own, and while he was relatively easier to defeat, the X-Men had best hope that the real deal never returns!
