King Ghidorah is a fictional monster, or kaiju, which first appeared in Ishirō Honda's 1964 film Ghidorah, the Three-Headed Monster. The monster was initially created by Tomoyuki Tanaka, Eiji Tsuburaya and Shinichi Sekizawa as an homage to the eight-headed mythological Japanese dragon Yamata no Orochi. Although the name of the character is officially trademarked by Toho as "King Ghidorah", the character was originally referred to as Ghidorah, Ghidrah or Monster Zero in some English markets.

Kaiju is a Japanese term that is commonly associated with media involving giant monsters. A subgenre of science fiction, it was created by Eiji Tsuburaya and Ishirō Honda. The term can also refer to the giant monsters themselves, which are usually depicted attacking major cities and battling either the military or other monsters.