Martin Mantle, Jr. was an engineer who turned into a serial killer known as Sportsman, due to his modus operandi.
As a kid, Martin was not interested in sports, which annoyed his father, who was a notorious scientist. Mr. Mantle developed a serum to improve his son's stamina and physical abilities and he used it against Martin's will. When his mother learned of this, she and Martin abandoned Mr. Mantle and moved away.
Martin grew up and the effects of his father's serum became notorious when he became a top athlete. After getting his engineering degree, Martin's health started to deteriorate and the doctors diagnosed him with a deadly disease, which was caused by his father's serum. Seeking revenge against society, Martin adopted the costumed identity of Sportsman and started killing top sports personalities until he was stopped by Batman.
- A large array of weapons concealed as sports items.
- This version of Sportsman, including all history and corresponding appearances, was erased from existence following the collapse of the original Multiverse in the 1985–86 Crisis on Infinite Earths limited series. Even though versions of the character may have since appeared, this information does not apply to those versions.
- 1 Appearances of Martin Mantle, Jr. (Earth-One)
- 1 Images featuring Martin Mantle, Jr. (Earth-One)
- Quotations by or about Martin Mantle, Jr. (Earth-One)
- Character Gallery: Martin Mantle, Jr. (Earth-One)