Most cartoon experts will claim that Hanna-Barbera's "super adventure" era began with Space Ghost, Frankenstein, Jr., & The Impossibles debuting in 1966. They would be wrong. The studio's first true superhero was Atom Ant, who preceded the others by a year, debuting on NBC. Superherocartoonsite uploaded the open, including theme vocals by actor Ted Cassidy (The Addams Family), to YouTube:
Howard Morris, who is better known for his role as troublemaker Ernest T. Bass on The Andy Griffith Show, and later would be the voice for Jughead on The Archie Show, was the original voice of Atom, but when our atomic insect joined the cast of Yogi's Gang, studio ace voice artist Don Messick took over the part. Morris had gone over to Filmation by then, of course, but there wasn't much difference. It can be said that Atom Ant was a take-off on Mighty Mouse, who was still going strong over on CBS at the time. Hanna-Barbera figured, we can make a smaller superhero work, and they did. However, because Atom was mostly played for laughs, and had two comedy features supporting him (Precious Pupp & Hillbilly Bears), it would be hard to reboot him as a more serious superhero character, though I'd not be surprised if someone actually tried.