Rather than face a live in prison for a crime he did not commit, Air Force captain Nathaniel Adam volunteered to take part in the top secret "Captain Atom Project". But an atomic explosion accidentally bonded a living alien metal to Adam and sent him hurtling forward in time to the modern day. The transformed convict was given a new lease on life as teh nuclear-powered DC super hero, Captain Atom.
Atom seemingly sacrificed his life to save Superman and Earth by piloting a starship to destroy a kryptonite meteor, but at the moment of his apparent death, Captain Atom experienced a time-shift resulting in his arrival in the Wildstorm Universe. During the interdimensional travel Atom absorbed a portion of the Void essence which altered his appearance, turning him from a silver color to a gold tint with red banding.*
*source = back of package, Superman/Batman, and Captain Atom: Armageddon.