King Ghidorah, also known as Monster Zero, is a three-headed dragon kaiju who first appeared in the 1964 Godzilla film Ghidorah, the Three-Headed Monster.
Having been featured in four films and a television series, the Showa King Ghidorah is the incarnation of the character with the most onscreen appearances to date. An evil extraterrestrial three-headed dragon, King Ghidorah attacked Venus over 5,000 years ago, effortlessly eradicating the planet's advanced civilization. In the 20th century, King Ghidorah arrived on Earth inside of a meteor and prepared to do the same to it. However, Mothra was able to convince Godzilla and Rodan to join forces with her to fight King Ghidorah off and send him back into outer space. In the year 196X, King Ghidorah was now terrorizing Planet X, and was known by the native Xiliens as "Monster Zero." The Xiliens convinced humanity to allow them to bring Godzilla and Rodan to Planet X, where they fought and defeated King Ghidorah once again.