John Walker grew up idolizing his older brother, Mike. Mike was a soldier and helicopter pilot who died in the Vietnam War. John wanted to honor his brother's memory by enlisting in the military.
After John left the military, he was told by a friend about the Power Broker, a mysterious individual who gave people superhuman abilities. Walker and his friend received the treatment, which granted the gifts of superhuman physical power.
As a result of the experimental mutagenic process conducted on him by the Power Broker, John Walker has superhuman strength. His endurance is also heightened albeit to a lesser degree. His speed, agility, dexterity, reflexes, coordination, and balance are of the order of a superior Olympic athlete.
This Collects the two series that he has starred in.