The Vision

 Real Name: None

The Vision was a synthezoid - a synthetic human android - who was created by the artificial intelligence Ultron to do his bidding.  Originally set against the Avengers by Ultron to gain a supply of adamantium, vibranium, and Captain America's shield, he managed to obtain two of this three goals before being defeated by the Avengers.

Repaired by Ultron, the Vision was sent against them again by Ultron in his bid to create robot replacements of the Avengers and transfer the consciousness of the Wasp into a robotic body named Jocasta, to serve as Ultron's mate.  The Vision ultimately turned against Ultron, siding with the Avengers.

Damaged, his form was rescued by Captain America.  The Vision was repaired, and joined the Avengers.