Jack of Hearts, originally Jack Hart, is the son of Marie Hart, a Contraxian alien/humanoid, and Philip Hart, a scientist who created the energy source known as zero fluid. One day, Jack was exposed to a vat of the zero fluid which caused a mutagenic change in his body and gave him superpowers.
He was created by Bill Mantlo and Keith Giffen and introduced in The Deadly Hands of Kung Fu #22 (March 1976). His accident gave Jack the ability to create concussive blasts, survive in space, and fly, as well as superhuman strength, increased intelligence, and he can sense motion.
Once he’d gained powers, Jack went on a mission to punish the Corporation that was responsible for his father’s death. That plan put him at odds with superheroes like the Hulk and the Sons of the Tiger. Eventually he tracked down Stryke, the one who murdered his father, and killed him.
Wanting to change his ways and become a superhero, he asked Tony Stark if he could become Iron Man’s apprentice. Iron Man agreed to take him on, and Jack teamed with him, Nick Fury, Jasper Sitwell, Guardsman, and Jean DeWolff to fight Midas. Jack helped Iron Man fight the Soviet Super-Soldiers and later the Rigellian Commander Arcturus. After learning from Iron Man, Jack went on to become a true hero in his own right.