The Jack of Hearts in its most usual sense is a Playing card.

Jack of Hearts (Jack Hart) is a fictional character, a superhero in the Marvel Comics universe. He first appeared in Deadly Hands of Kung Fu #22.

Jack is the son of Philip Hart, a scientist who created Zero Fluid, and Marie, an alien humanoid woman of the Contraxian race. After being exposed to a vat of Zero Fluid, Jack underwent a mutagenic change and gained the ability to project concussive energy from his body. After gaining these powers, Jack began his mission of vengeance against the Corporation that killed his father. This led to Jack fighting other superheroes such as the Sons of the Tiger and the Hulk.

Later, Jack moved past his blind mission of vengeance and became a true superhero, working with various superheros such as the Defenders, the Thing, Quasar, Spider-Man, Moondragon and the Silver Surfer. Eventually he joined the Avengers, becoming the fifty-second superhero to join.

In Avengers volume 3 #76 (aka #491, due to renumbering), Jack of Hearts chose to commit suicide rather than continue living in containment 14 hours a day. Jack took a child murderer who had abducted the second Ant-Man's daughter along with him so that they both die when Jack explodes in space.

In #85 (aka #500), Jack reappeared just long to blow up himself, the Avengers mansion, and Scott Lang (Ant-Man). This Jack may have been some type of "apparition" created by an insane Scarlet Witch rather than the actual Jack of Hearts; either way, he is still quite dead.