The Martian Manhunter known as J'Onn Jon'zz, in his alter ego of police detective John Jones on his adopted world of Earth-One, was aided by his fellow police officer Diane Meade, with whom he developed budding romantic feelings for.
Over on Earth-Two, Diane's cosmic twin was socialite Joan Carter. Joan was the former fiancee of scientist Robert Crane, who's humanity ended when his mind was placed in the metallic casing of Robotman following his human body's death.
Despite sharing several adventures with their seclusive superhero inhuman boyfriends, both the Manhunter and Robotman decided to abandon their relationship with the ladies in their lives, resolute on their determination to aid humanity in an effort to obtain humanity for themselves. Both would leave their respective Earths behind, with what became of Diane and Joan a mystery henceforth.