Created by the villainous Ultron to destroy the Avengers, the Vision rebelled and instead joined the team. Given that he was created with the brain patterns of the deceased Wonder Man, its not that surprising that the two characters have very similar introductions to the team. The Vision is a synthezoid, an artificial man that was believed to have once been the body of the original Human Torch (this was retconned and later retconned again, and the current explanation is that the time traveling Immortus used the Forever Crystal to split the Torch into two entities). After betraying Ultron, the Vision joined the Avengers and began a relationship with the Scarlet Witch, eventually marrying her. After joining the West Coast Avengers, the Vision became team leader for a period. He later became unbalanced and tried to take over the worlds computers, which led to the government dismantling him. When rebuilt, the Vision was left emotionless as Wonder Man refused to allow his brain patterns to be used again. Eventually regaining his emotions, the Vision was subsequently destroyed during the events of Avengers Disassembled, but was later rebuilt by Tony Stark. Unfortunately, despite the characters 417 appearances, hes been largely ignored in the current Avengers comics. We can only hope Paul Bettanys upcoming portrayal of the character in Age of Ultron will lead Marvel to return one of the greatest Avengers to the team.
Percival Constantine is the author of several novels and short stories, including the Vanguard superhero series, and regularly writes and comments on movies, comics, and other pop culture. More information can be found at his website, PercivalConstantine.com