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.
Doctor Hartford Jackson was likewise an accomplished amateur inventor, living in Keystone City, and as such developed a thinking cap that also intensified the mind's energies. However, his cap was stolen by criminal Tricky O'Reilly and used against the Flash, before the crook was finally defeated and the cap returned to its owner.
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.
As for the thinking cap... it would seem that it ended up in the hands of a famous felon on Earth-Two,. When malevolent mastermind the Thinker procured the device, he eventually modified it to torment the Scarlet Speedster and his allies of the Justice Society, both on his own and as a member of the Injustice Gang. When none of his schemes proved successful even with this wonderful gadget at his disposal, the Thinker finally retired from crime for good.