King Ghidorah is a three-headed alien dragon and Godzilla's arch-enemy, he is depicted in many different versions/forms in the Godzilla series. Most versions of King Ghidorah have powers including flying, surviving in space, and spitting gravity beams.
The Different Forms of Ghidorah
Just regular ol' King Ghidorah. Introduced in the 1964 film, Ghidorah, the Three-Headed Monster.
As seen in the 1991 Godzilla vs. King Ghidorah, Dorats are the form of King Ghidorah before they were exposed to radiation. Three Dorats are left in the past to combine and mutate into King Ghidorah from radiation.
Mecha King Ghidorah
As seen in the 1991 Godzilla vs King Ghidorah. A cybernetic King Ghidorah with one head and part of body replaced by machine parts.
As seen in Rebirth of Mothra. Desghidorah's true form is living, shapeshifting lavas from space. He copies features from reptiles on earth and thus becomes a dragon-like monster. Desghidorah can manipulate fire and lava.
Cretaceous King Ghidorah / Grand King Ghidorah
As seen in Rebirth of Mothra 3. A space monster who lived over 200 million years, he used to do mass genocides on many planets. He is implied the ancestor of King Ghidorah and the first evil Ghidorah in the species.
As seen in the 2001 Godzilla, Mothra, King Ghidorah: Giant Monsters All Out Attack. This version of Ghidorah is an earth defender, unlike most versions being invaders.
Monster X / Keizer Ghidorah
As seen in the 2004 Godzilla: Final Wars, Monster X is an alien monster that is quite human in appearance. It looks nothing like King Ghidorah until he evolves and transforms into Keizer Ghidorah. Keizer Ghidorah has four legs as opposed to the usual two and has a much darker body color.
King Ghidorah in the Movies
Since King Ghidorah's debut in 1964, it has been in 5 films. All were distributed under the Japanese film studio, Toho. Listed below are Toho's official English title for all the films, along with their original release date.
12.20.1964 - Ghidorah, the Three-Headed Monster
12.19.1965 - Invasion of Astro-Monster
08.01.1968 - Destroy All Monsters
03.12.1972 - Godzilla vs. Gigan
12.14.1991 - Godzilla vs. King Ghidorah
1996 - Rebirth of Mothra
1998 - Rebirth of Mothra III
12.15.2001 - Godzilla, Mothra and King Ghidorah: Giant Monsters All-Out Attack
12.04.2004 - Godzilla: Final Wars