Johnny was a silent film actor, but after being forced into retirement by the then-new "talkies," he turned to a life of crime. He would eventually come into possession of a "Subspace Prototype", that enabled him to become intangible.
A brilliant scientist, Doom was once a classmate of the Fantastic Four's Reed Richards. However, he became embittered by his jealousy of Richards and by facial scars received from an experiment gone awry.
Hawkman was Carter Hall, a reincarnation of an ancient Egyptian prince, who had in the modern day discovered that the mysterious "ninth metal" could negate the effects of gravity and allow him to fly. He donned a costume with large wings to allow him to control his flight and became the crimefighter, Hawkman. An archaeologist by trade, Hall uses ancient weapons from the museum of which he was curator in his efforts
Mephisto delights in exploiting humanity's belief in a singular figure of evil, the biblical Satan, and has often posed as this entity in order to strike deceptive bargains with unwitting human, providing them with their desires in exchange for their souls. Mephisto draws power from captive souls, and often targets those who are particularly powerful, or exceptionally pure.
The boy who would become Black Manta was an autistic youth who grew up in Baltimore, Maryland, and loved to play by the sea. As a youth he was kidnapped and forced to work on a ship for an unspecified amount of time.
Mark Raxton developed an experimental new metallic alloy for the Spider-Slayers from a radioactive meteor, but Raxton attempted to steal it and sell it for his own profit. In the ensuing fight with Smythe spilled it all over himself, his skin absorbing it and turning golden.
Leonard Samson had been working on Banner/Hulk in his job as a psychiatrist—exposed himself to some of the siphoned radiation, causing his hair to become green and granting him superhuman strength proportionate to its length, reminiscent of his biblical namesake.