Jack Lansing became Jack Diamond when he was given the black diamond of power set in a gold ring by an old mystic from the Far East. With the ring Jack is able to form anything his mind can imagine. He has super strength, invulnerability, super senses, the ability to heal others. He can shoot bolts of lightning and energy. He can also fly. His power over the ring is based on his concentration and force of will just like the Green Lantern. That said Diamond Jack was published before the first appearance of Green Lantern in All-American Comics.