Invasion of Astro-Monster (怪獣大戦争, Kaijū Daisensō, lit. The Giant Monster War) is a 1965 kaiju film directed by Ishirō Honda, with special effects by Eiji Tsuburaya. It is the sixth film in the Godzilla franchise and Shōwa period. The film was a Japanese-American co-production; it was the second collaboration between Toho Studios and UPA. The film stars Akira Takarada, Nick Adams, Kumi Mizuno, Akira Kubo, and Yoshio Tsuchiya, with Haruo Nakajima as Godzilla, Masaki Shinohara as Rodan, and Shoichi Hirose as King Ghidorah. In the film, aliens plead with humanity to borrow Godzilla and Rodan to defeat King Ghidorah, only to betray the humans and unleash the monsters on the Earth.
Invasion of Astro-Monster was released in Japan on December 19, 1965 and received a theatrical release in the United States on July 29, 1970 by Maron Films as Monster Zero, on a double feature with The War of the Gargantuas.