Real Name: Ultron  or Ultron - 13, Ultron - 18 or whatever number designation it gives itself

First Appearance: Avengers #54 (1968)

Powers: With an adamantium shell or body (the same material as Wolverine's unbreakable claws and bones), Ultron is almost indestructible which is one reason different versions of his pesky surviving head keep resurrecting him over the years. While not invulnerable (those joints must have some flaws), Ultron can transfer his memory bank to other computers, robot bodies or hide within other programs until figuring out a way to reconfigure and destroy humanity.  The robot's more conventional powers include super strength, energy blasts, super speed and self-repair.

Hero or Villain: Villain

Why: No doubt the greatest Avengers villain of all-time, you could argue the team fears no adversary more.  Created by founding member Hank Pym (Ant-Man, Yellowjacket, Giant-Man) for peaceful purposes, Ultron rebelled against its "father" and has made his team, The Avengers, one of its primary targets.  He also created the Vision, who rebelled against Ultron and became a hero and member of the Avengers. Needless to say, there is a lot of history between the super hero group and Ultron to mine on the big screen.