Adam II was an android life-form originally created by Phinneas T. Horton, the creator of the original Human Torch. Adam II was Horton's attempt to replace and improve upon the Torch, who had abandoned his master to join the Invaders' fight against the Axis powers of World War II.
Ironically, it was Torch's first return to his creator that caused the team to stumble onto Adam II. The android had imprisoned his creator and made his own gang of mindless androids to help him conquer humanity. His initial plan was to replace then-Senate candidate John F. Kennedy with an android duplicate. The Invaders defeated Adam II, but not before the villain's thugs crushed William Naslund (the second Captain America) to death.