Development In the early 1960s, special effects technician
Willis H. O'Brien (who provided the
stop motion animation for the 1933 film
King Kong) proposed an idea for a new
King Kong film to be filmed in color. O'Brien wrote a story outline titled
King Kong vs. Frankenstein and succeeded in obtaining permission from
RKO Pictures attorney Daniel O'Shea to use the King Kong character. O'Shea then introduced O'Brien to film producer
John Beck to help secure funding. With a completed script by
George Worthing Yates (retitled as
King Kong vs. Prometheus, in reference to the
original Mary Shelley book), Beck generated some interest in Hollywood but failed to secure funding and reached out overseas. Behind O'Brien's back, Beck succeeded in striking a deal with Japanese studio
Toho Co., Ltd (producers of the 1954 film
Godzilla) to produce
King Kong vs. Prometheus. Toho was only interested in acquiring the King Kong character and the project was redeveloped into
King Kong vs. Godzilla. O'Brien attempted to sue (presumably Beck) over the deal with Toho but dropped the lawsuit due to mounting attorney fees and died on November 8, 1962. Shortly after the release of
King Kong vs. Godzilla, Toho began work on a film that would potentially feature the Frankenstein monster, or simply named "Frankenstein". Inspired by a story concept by
John Meredyth Lucas (who wrote the American localizations for three of Toho's films), Toho conceived of
Frankenstein vs. The Human Vapor and tasked
Ishirō Honda to direct and
Shinichi Sekizawa to write the script. Sekizawa failed to finish the story treatment, citing lack of inspiration, and abandoned the idea. In 1964, Honda traveled to the United States to help finalize a deal with
Henry G. Saperstein and his
United Productions of America (UPA) studio. The deal would see UPA co-producing three films with Toho, with "the right of final decision" on the film by Honda. The deal also allowed Saperstein to attach Hollywood actors as the leads, to provide half the financing for territorial rights, and consultation on the scripts. One of the films to be co-produced under the deal would be
Frankenstein vs. Godzilla.
Writing The idea for
Frankenstein vs. Godzilla originated from UPA, with
Jerry Sohl and
Reuben Bercovitch providing the initial concept. Both writers retained credit for the story, but it is unclear how many of their ideas were retained in the final film.
Takeshi Kimura's first draft, dated July 3, 1964, features many of the same elements in the final film. The story dealt with the heart of the original Frankenstein monster becoming irradiated and growing into a giant Frankenstein monster. Afraid the giant would start eating people, Godzilla would be awakened from slumber in the Kurile Trench by the JSDF and goaded into a fight with the monster in hopes of destroying him. The story would end with natural disasters defeating the monsters as Godzilla disappears into a raging river flow and the giant Frankenstein monster disappears into magma caused by an erupting volcano. A March 1965 draft replaced Godzilla with new
kaiju Baragon, and the final draft from May 10, 1965 had Frankenstein acting like less of a monster, with the human characters fostering compassion for him. Honda criticized the decision by Toho and UPA to include a
kaiju, calling it "convenient", and originally wanted to explore the tragedy and immoral science behind Frankenstein instead.
Pre-production Nick Adams was handpicked by Saperstein for the lead. Several crew members spoke fondly of Adams, who would amuse his fellow co-stars and crew with stories from Hollywood. Co-director Koji Kajita regaled that Adams became good friends with Honda and
Yoshio Tsuchiya, often teasing them and them teasing Adams back. Despite being married, Adams flirted openly with
Kumi Mizuno and called her on the phone every night. Mizuno admitted that Adams was "headstrong" and that she had to "get out of that situation", but stated it was "fun" to work with him. Adams delivered all of his lines in English, while everyone else delivered their lines in Japanese. Koji Furuhata earned the role of Frankenstein through an open audition. Furuhata wore green contact lenses to emulate a Caucasian look, a flat-head prosthetic and brow resembling
Jack Pierce's Frankenstein Monster design and large shirts and loincloths. Honda had originally wanted to explore more of the science-gone-wrong theme, but was forced to change the story in the middle to reach a climactic monster battle.
Alternate ending Saperstein had requested an alternative ending for the international release in which Frankenstein battled a
giant octopus, who eventually defeated Frankenstein by dragging him into a lake. This resulted in the cast and crew being reassembled after principal photography and post-production had wrapped, as well as building a new set and building a new prop to represent the giant octopus from foam, latex and sawdust initially moulded over a wire frame for support during construction. Despite filming the new ending, Saperstein ended up cutting it regardless because he believed the giant octopus "wasn't that good". When the film was in production, trade magazines listed this film's title as
Frankenstein vs. the Giant Devilfish. Honda had stated that the reason why the giant octopus ending was initially requested was because the American co-producers were "astonished" by the giant octopus scene in
King Kong vs. Godzilla and wanted a similar scene in this film. Honda also confirmed that various endings were shot, stating: "In fact Mr. Tsuburaya had shot five or six final scenes for this film. The infamous giant octopus is only one of these endings." Honda also expressed that the alternate ending was never intended to be released on the Japanese version, stating: "there was never any official plan to utilize the sequence; but an alternative print with that ending was accidentally aired on television surprising many Japanese fans because it was not the ending they had remembered from the original theatrical release." ==Release==