Ultron

Ultron was originally a robot created by Hank Pym, the Ant-Man, to be the ultimate superhero. However, Ultron became fully sentient, and rebelled against Pym. Seeking nothing but Pym's destruction. As part of Ultron's mad rampage, he created the android Vision. Vision too became fully sentient and rebelled against Ultron, warning the Avengers of Ultron's scheme to attack the president. Ultron fought a tremendous battle against the Avengers ending in his own destruction.

Remnents of Ultron later resurfaced in Japan, posing another major threat to the Avengers. He battled the Avenngers once more and again was defeated.Vision later became obessesed with finishing off Ultron and uses himself as bait to lure Ultron out. The plan worked a little too well. Ultron attacked and almost destroyed Vision. When the Avengers showed up, however, Ultron was destroyed once and for all.

This version of Ultron remains relativley faithful to the Ultron in the comics. However, in the comics, Ultron falls in love with the Wasp. After learning that the two could never be, he creates Alkhema, another fully sentient robot. In this show, Ultron seems to focus all of his rage at Hank Pym and Vision, while in the comics it was directed to all humanity.