Psychiatrist Steve Dayton was among the richest men on Earth-One. A profession psychiatrist and highly skilled inventor, his passion was actress Rita Farr, aka Elasti-Girl. In order to secure her attention and affection, as she had been recruited into the crime-fighting team known as the Doom Patrol of Midway City, Dayton became a superhero himself. As Mento, Dayton utilized the awesome energies of his mind amplified by his specially designed helmet to become Midway's other resident hero, after the Patrol as well as the Winged Warriors, Earth-One's Hawkman and Hawkgirl, whom he never had occasion to meet.
Kirk Jason was an archaeologist assistant who was the latest heir in the line of the Immortal Man. on Earth-Two. Deriving his mental power and long lifespan to a mysterious iron ore meteor fragment that an ancestor Klarn had discovered eons before, Jason has a short lived career as a secret protector of the innocent.
Eventually, Dayton wed the object of his affection, yet sadly shortly thereafter Rita and her teammates perished protecting a small community. Steve would revive his Mento alter ego in order to hunt down the villains who killed his wife, and briefly turned insane before his step-son Changeling helped him recover his senses. Jason perished in battle versus a shape changing creature. But another Immortal Men would take his place shortly thereafter.