Jet Jaguar was the earliest example of a fan-service in a Godzilla film, the result of a contest Toho had in mid-to-late 1972 for children to come up with a new hero for them to use (to capitalize on the many tokusatsu and anime superhero and super robot shows that were all the rage at the time). The winner of the contest was an elementary school student, who submitted the drawing of a robot called Red Arone, which superficially resembled both Ultraman and Majingâ Zetto (1972) (both of which were very popular at the time). The robot was renamed "Jet Jaguar" and was set to star in a film vehicle for him, titled "Jet Jaguar vs. Megalon," which pitted him against Megalon (a previously unused Godzilla enemy design). However, Toho figured Jet Jaguar would not be able to carry the film on his own, either in screen appearance or marketing value (which was very important to Toho), so they shut the project down during pre-production after doing some tests and storyboards. Less than a month later, screenwriter Shin'ichi Sekizawa was called in to rewrite the script to add Godzilla and Gigan, providing more marquee value (especially since Godzilla was still very popular with children). After revised pre-production, shooting took a hasty three weeks to make up for lost production time. Due to this delay, the total production time, from planning to finish, was six months.
According to Teruyoshi Nakano, the Godzilla suit used in this film (nicknamed the "Megaro-Goji" suit) was made in a week, making it the fastest Godzilla suit ever made to date. They didn't have time to make the eyes work correctly, something they had more time to fix for Godzilla's appearances on Toho's superhero TV series Ryusei Ningen Zon (1973), which was produced around the same time.
Gigan's design was noticeably altered compared to the previous film. This is because it's an entirely different suit, as the original supposedly got too damaged. He now has a much larger head and a less fierce expression, he has golden scales around his neck, his limbs appear shorter, his back sails are pointier, and he looks overall stockier. He doesn't demonstrate his signature buzzsaw embedded into his torso either (apart from stock footage), since that function was removed from the suit. This version of the suit was used for Gigan's appearance in the television series Ryusei Ningen Zon (1973).
This film was originally produced in 1973 but was not released in the United States until 1976. A small US distributor, Cinema Shares International, hoped to ride on the popularity of 'Dino De Laurentiis' 's highly promoted production King Kong (1976). This became especially apparent in the US poster art, which depicted Godzilla and Megalon battling each other on top of the World Trade Center towers.
The only Godzilla movie not to feature any female characters. The only women in the film are the dancers we briefly see in Seatopia.
Megalon was originally created to be the third evil monster (besides King Ghidorah and Gigan) in War of the Monsters (1972) (in its second draft, "Godzilla Vs. the Space Monsters: The Earth Defense Command"), but budgetary cuts nixed Megalon from that film altogether. While he was originally created to be an opponent for Godzilla, he was considered for the role of the lone villain of this film when it was planned as a Jet Jaguar solo vehicle ("Jet Jaguar Vs. Underground Monster Megalon"), before, ironically, Godzilla was written into the story along with Gigan.
Aside from playing the Seatopian Emperor Antonio, Robert Dunham, who was also a stuntman and vehicle racer, also played one of the two the "Unit 1" Seatopian Agents (he was the one on the motorcycle) in one of the car chase scenes (where he and another agent were chasing Yutaka Hayashi's character). The last shot where he gets splashed on with cement was done with another actor, because Dunham had to get to the studio that day to record his part, and didn't want to have to get cleaned up on the way.
Megalon's ray beam is animated the same way as King Ghidorah's gravity beams. This was made to ensure that stock footage from Ghidorah's movies could easily be interspliced between shots of Megalon firing his beam.
Although regarded as the worst of the original series, in 1977 it became the only Godzilla film to be shown on American network television. It was presented on the NBC network in an edited version hosted by John Belushi dressed in a Godzilla costume.
In the German version of the movie, the robot Jet Jaguar is called King Kong. According to rumors, they even claim that he is supposed to be the giant ape wearing a robot suit, but that is false. The dub merely calls him King Kong, but no reference is made to him being anything other than a human-built robot. The reason for this is that the distributors probably wanted to ride the popularity of the King Kong brand. Curiously, the evil robot Mechagodzilla from the following movie, who has no connection to the benevolent Jet Jaguar, is also called King Kong in Germany.
Despite widely being considered one of the weakest entries in the Godzilla series, the movie actually received positive reviews by certain American critics upon its initial release in the States, who praised the effects work and the miniatures. In actuality, much of the movie's special effects were rather lazily cobbled together from stock footage taken from earlier films made by Toho Studios.
Due to its publicity and wide availability in the United States, this movie is often regarded as one of the main reasons why the Godzilla franchise has become so ridiculed in the west. Its American distributors, Cinema Shares International, built up a large advertising campaign around the movie, and in 1977 a drastically shortened version of the film premiered on prime-time TV on the NBC network, attracting many viewers. This is also the only Godzilla movie whose VHS release has fallen into public domain, making it more easily accessible and adding to the movie's notoriety in the US.
Some inadvertent nudity popped up in the film courtesy of the centerfolds in the kidnappers' truck. The centerfolds are of Playboy Playmates Gloria Root (December 1969) and Deanna Baker (May 1972).
The retired Florida independent wrestler Brian Bernick used the name Jet Jaguar.
The story outline was composed by Shin'ichi Sekizawa, one of the Godzilla series' most prolific writers, but the actual script was written by director Jun Fukuda and completed just before filming began.
Megalon is one of two villain monsters that survives in the continuity of the original Godzilla movie series. The other is Ebirah from Ebirah, Terror of the Deep (1966). Gabara from Gojira-Minira-Gabara: Oru kaijû daishingeki (1969) does not count, as he only existed in the dreams of a young boy.
As in the previous movie, Gigan flees from the climactic fight and survives. He would reappear as a guest star in the Ryusei Ningen Zon (1973) TV series, in which he is finally killed through the combined efforts of Godzilla and Zone Fighter.