In the fall of 1966, Sy Fischer, a television agent who at the time worked at the powerful Ashley Famous Agency where his job was to sell shows on behalf of his clients, one day noticed his son Stuart reading a Fantastic Four comic book. Fischer saw potential in the Fantastic Four when he asked his son if this comic book could be a good cartoon who enthusiastically said, "Yes!" The very next day, Fischer got on the phone with Joseph Barbera, the co-founder and head of Hanna-Barbera and told him of this wonderful comic by Marvel Comics and recommended that Hanna-Barbera get the rights to develop it for Saturday morning. After taking a look at the FF, Barbera agreed. Both Joe Barbera and Sy Fischer then contacted Stan Lee and asked if the rights were available and luckily enough they were. A deal was quickly made between the two companies and Hanna-Barbera put the show into development and pitched it to ABC, and quickly it was on the ABC Saturday morning schedule for the Fall of 1967.
Marvel had a very good year in 1967: "The Marvel Super Heroes" was still going in syndication, and it introduced two shows on network Saturday morning television: The Fantastic Four, done by Hanna-Barbera, and Spider-Man done by Krantz Films. Fantastic Four began one half-hour before Spider-Man, debuting on September 9, 1967 at 9:30 in the morning, with Spider-Man following at 10:00 A.M.
Namor the Sub-Mariner never make an appearance on this cartoon due to starting in his own cartoon segment on "The Marvel Super Heroes" (1966) by Krantz Films. Dr. Gamma, the evil scientist that mutates into a creature called Gamma Ray and Prince Triton of Pacifica who fought against Warlord Atuma were original creations by Hanna-Barbera to take the place of Namor the Sub-Mariner when adapting "The Fantastic Four" issues #4 and #33 respectively. The Fantastic Four could not appear on the Sub-Mariner cartoon segment and were replaced by the X-Men (who were referred to as the Allies for Peace).
This show was expertly done and very loyal to the comic book at the time. Hanna-Barbera and ABC retained Stan Lee and Jack Kirby as consultants. Designing the show was Alex Toth, an artist involved in both animation and comics. His work was well received by both professionals and fans, doing the Fabulous Foursome justice on the small screen. Characters from the comics were used in the show, including the Super-Skrull, Klaw, and the Mole Man, as well as a few original characters and stories created by Hanna-Barbera.
On the stories adapted from the comics, the small print on the title cards for each individual episode actually gives credit to the specific comic issue it is adapted from.