Jack Winters first appeared in X-Men #39, and was created by writer Roy Thomas and artist Werner Roth. Jack's name and appearance were likely based on famous actor Jack Nicholson.
Jack O'Diamonds, or the Living Diamond, was a mutant villain whose hands were turned into a flexible, diamond-like substance after he was exposed to atomic radiation during an accident at the lab where he worked. He later managed to transform his entire body into "living diamond" through further exposure to radioactive material. Jack also possessed telepathic abilities that allowed him to bend people to his will.
Winters tried to convince a young Scott Summers to join him in crime, but Professor X intervened and saved Scott. Together they defeated Jack using a vibration beam. Scott was then recruited by Xavier to enroll at the Xavier School for Gifted Youngsters and become the first X-Man.
Coincidentally, Cyclops would later become close to another mutant that possessed telepathic powers and the ability to turn themselves into organic diamond (as well as a "cold" name): Emma Frost.
Years after he'd been defeated by Cyclops and Xavier, Jack fought She-Hulk as a zombie. The villain Black Talon resurrected four mutants from their graves to aid him: Jack Winters, the Changeling, Harry Leland, and Scaleface. Black Talon labeled this group the X-Humed, and ordered them to attack the She-Hulk. Black Talon was eventually defeated and the four zombies returned back to their graves.
Powers and Abilities
After being exposed to radioactive isotopes in a lab accident, Jack's skin was mutated to become a diamond-like substance. This granted him a degree of superhuman strength and resistance, allowing him to break steel beams with his diamond hands. After further exposure to radiation his entire body became flexible diamond alloy, allowing him to withstand optic blasts from a young Cyclops.
Jack possessed mild telepathic abilities, allowing to sense the presence of others as well as send out mental suggestions to bend people to his will. He could also block out telepathic assaults from Professor X.
Jack could teleport himself and others short distances by separating the atoms in their bodies and recombining them at their destination.