Produced by Hanna-Barbera Productions in the mid 60s, Fantastic Four (or Fantastic 4 as it is sometimes seen) is the first cartoon to feature the popular Marvel comic team.
The characters were designed by Alex Toth, who did a lot of character designs for Hanna-Barbera action shows in that era, including Super Friends, and the plots were taken directly out of the comics.
The 20 episode run first ran on September 6, 1967 on ABC on the same day as another new show, Spider-Man. While Spider-Man went on the be one the most well-known cartoons in history, Fantastic Four was canceled after 20 episodes and remains relatively obscure. The show later aired as part of Hanna-Barbera's World of Super Adventure.
Human Torch - Jack Flounders
Invisible Girl - Jo Ann Pflug
Mr. Fantastic - Gerald Mohr
Thing - Paul Frees
Watcher - Paul Frees
Doctor Doom - Joseph Sirola