His past was unknown except for the fact that he was experimented on by the government due to having latent mutancy. However, he couldn't control his awakening powers. It was reported that he was killed and his body destroyed, but this wasn't the case.
This Captain joined up with the Six, and helped protect mutants from SHIELD.
He later joined the Six in crossing the Canadian border to aid Wolverine, but they were intercepted by the Avengers to prevent the Six from possibly starting a war. The Avengers' leader Black Widow held Captain America with disdain because they used to be in a relationship and he ran on the Avengers during a time of need. When negotiations broke down, the two teams fought each other. That was when Captain America's powers started to go out of control. He took out most of the Six as well as his fellow Avengers.
Captain started losing his mind and ranted that he needed to destroy America's enemies. During his rampage, he killed the Avengers and the Canadian forces sent to stop him. In the end, Havok was able to kill Captain. After his death, Captain's body was taken by the Beyonder, who had been sleeping in the Earth's core until he was awakened by Captain's out of control powers. He fed off Captain's remaining energy and read his mind to learn more about Havok.
* Heightened strength, energy projection with mutant powers
After being given the Super-Soldier Serum, Captain America presumably possesses powers similar if not comparable to his predecessor. His mutant powers include the ability to increase his mass and strength, telepathy, force field, immense energy powers, and near-invulnerability.
Captain reacted badly to the Super-Soldier Serum he was given, making him insane and causing his mutant powers to flare out of control.