Double Header hales from the world of Janus were the inhabitants start as conjoined twins. He headed to Earth to try out for the Legion of Super-Heroes in the 30th Century.
Doubleheader first appeared in the pages of Adventure Comics #323, August 1964.
Original Continuity: New Earth
Frenk and Dyvud Retzun were from Janus, a world where a species starts as conjoined twins and eventually split into two identical beings. While this is an interesting biological process, it isn't exactly an impressive power. This fact, along with Frenk and Dyvud's inability to cooperate, led to the Legion's choice to reject Double-Header. The pair joined the Legion of Substitute Heroes, in an auxiliary status, but showed up for meetings infrequently. They did, however, manage to make an appearance at the Wedding Ceremony of Bouncing Boy and Duo Damsel.
5 Years Later; Five Year Gap
During the Five Years Later storyline, Frenk and Dyvud were no longer with the Subs. They were instead living in wealthy retirement off of residuals from from their sitcom "Getting Ahead".
Retroboot: New Earth
Frenk and Dyvud apparently stayed on with the Substitutes, in the recently revealed continuity in Action Comics. It was mentioned that he was killed in Earth-Man's assault on the Subs, but this was never shown on-panel.
Powers and Abilities
Doubleheader derives his "powers" from his native born physiology that all Janusian's of his planet have, born as a conjoined twin. Having two heads and able to divide into two bodies as they mature Doubleheader has inhibited this natural mechanize to keep this psychical advantage. Using this unique trait Double header has become quite skilled in very specialized personal hand-to-hand combat skills.
As a member of the Legion of Substitute Super-Heroes Double header has been given a Legion Flight Ring. Various abilities come equipped with the ring. A signal device, a long rang communicator, navigation system, and of course it grants the wearer the ability to fly.