In 1963, Fred Ladd, while working on the animated feature Pinocchio in Outer Space and on the animated TV series The Big World of Little Adam had seen artwork of Mitsuteru Yokoyama presenting a giant robot remote-controlled by a young boy. The Tokyo-based artist had designed the robot for a Japanese shōnen manga series Tetsujin 28 and later a black-and-white animated TV series called Tetsujin 28-go.[citation needed]

Ladd, who had produced the successful international, English-language adaptation of Astroboy, and Al Singer formed a corporation called Delphi Associates, Inc. in order to produce and distribute an English-language version of Tetsujin 28-gō. They took only 52 episodes of the Japanese series for the American market, and renamed the series Gigantor. Peter Fernandez wrote much of the English script, and participated in the dubbing. The series became an immediate hit with juvenile audiences, though adult reactions were sometimes hostile.[citation needed]

It was playing at 7:00 p.m. on New York's WPIX-TV in January 1966 when Variety gave it a particularly scathing review, calling it a "loud, violent, tasteless and cheerless cartoon." which was "strictly in the retarded babysitter class."

The reviewer added that Gigantor was popular; he said "Ratings so far are reportedly good, but strictly pity the tikes and their misguided folks."[4]

Gigantor became a popular Japanese export during this time. The series was shown in Australia on Melbourne television in January 1968 through Trans-Lux, on ATV-0 at 5:00pm. It was described by the TV Week as an "animated science fiction series about the world's mightiest robot, and 12-year-old Jimmy Sparks who controls the jet-propelled giant." The series aired in other markets around Australia, including Sydney, New South Wales on TEN-10, and in Adelaide, South Australia on SAS-10, (its debut on Monday October 28, 1968 at 5.55pm).[5] It was also screened in New Zealand around the same time.

Gigantor was one of a number of Japanese TV series that enjoyed strong popularity with young viewers in Australia during the 1960s. The first and undoubtedly the most successful of these was the hugely successful live-action historical adventure series The Samurai, the first Japanese TV series ever screened in Australia, which premiered in late 1964. It was followed by a contemporary ninja-based live action espionage series, Phantom Agents, and a number of popular Japanese animated series including Astro Boy, Ken The Wolf Boy, Prince Planet, Marine Boy and Kimba the White Lion, the cartoon series which is reputed to have been the uncredited basis for Disney's The Lion King.

In July 1994, Fox Family Films, a division of 20th Century Fox, acquired the rights to "Gigantor" for a live-action motion picture.[6] Anticipating that Gigantor would become a franchise for the studio, Fox tapped screenwriters Steve Meerson and Peter Krikes to prepare the script and budgeted between $35 million and $50 million for the film.[6] Executive producers Fred Ladd and Aeiji Katayama indicated that Mitsuteru Yokoyama would get an executive producer credit and that the 50-foot robot would be updated and modernized for the 1990s with a 12-foot height and morphed and computer-generated features.[6] However, the project has yet to come to fruition and Mitsuteru Yokoyama has since died.