El Dorado

Nope, just appeared. They rarely did origin stories with e few exceptions: Superman, in "The Planet Splitter" (original series); Green Lantern, Wonder Woman and Apache Chief (Challenge of the Superfriends); Batman (Sper Powers team: Galactic Guardians). I'd have to check my discs, but I can't recall if they covered Cyborg's origin in Galactic Guardians; I don't think so. Firestorm's background was covered in this show (Legendary Super Powers Show). We didn't get one for Black Vulcan or Samurai, either.

"Fortunately, Ah keep mah feathers numbered for just such an emergency!"