Keizer Ghidorah

"Well now, let's enjoy the main event, the last chapter in the Godzilla saga!"

- X before unleashing Monster X/Keizer Ghidorah Keizer Ghidorah, also known by his previous form named Monster X, is the main Kaiju antagonist and overall the secondary and later final main antagonist of the 2004 50th Anniversary Godzilla Movie, Godzilla: Final Wars​.

He is an enormous three-headed dragon kaiju used by the Xiliens to conquer the Earth and kill Godzilla. He first appears as Monster X and aids Gigan in battling Godzilla before later becoming Keizer Ghidorah, his final form which is based off of the popular archenemy of Godzilla, King Ghidorah.

He is 140 meters tall, 200 meters long and weighs 100,000 metric tons. As Monster X, he is 120 meters tall, 180 meters long and weighs 60,000 metric tons.

Godzilla: Final Wars
Monster X was called down to Earth by the Xiliens so as to take care of Godzilla. Descending to Earth in a meteor, the King of the Monsters and Monster X began battling each other. Though this new opponent had the advantage at first, the fight came to a standstill. Mothra appeared and Gigan was sent in to aid Monster X. Gigan quickly defeated Mothra and teamed up with Monster X to begin to overcome Godzilla. However Mothra returned and attacked Gigan, the two eventually finishing each other off. This left Godzilla and Monster X to face one another with the King of the Monsters managing to pummel him. Eventually their beam attacks collided and knocked them both off their feet. Godzilla got to his feet to watch Monster X undergo a terrible transformation into Keizer Ghidorah.

This horrifying space monster blasted his enemy with his gravity beams, using them to knock him to the ground, and then drag him all around the city. Keizer Ghidorah then sank his fangs into Godzilla, absorbing the King of the Monsters' very life force. However the Gotengo fired a beam at Godzilla that gave him the power of Keizer, an ancient energy that greatly increased the abilities of the one who possessed it. This allowed the King of the Monsters to free himself of Keizer Ghidorah's grip and blast him with his energized atomic blast, severing one of his heads. Keizer Ghidorah attempted to blast Godzilla with a gravity beam, but Godzilla pulled his other head in the path of the beam, severing it as well. Godzilla then tossed the maimed Keizer Ghidorah up and down before hurling him into outer space and blasting him with his red spiral atomic beam, destroying him for good.

Godzilla
Monster X is a major antagonist and the Bigger Bad in the comic series Godzilla by IDW. Monster X and his fellow space monsters SpaceGodzilla, Hedorah, and Gigan invaded the Earth, forcing the United States military to free the various kaiju contained on Monster Island so they could fight the space monsters off. Monster X attacked New York City, where he was intercepted by Mothra. After defeating Mothra, Monster X was attacked by Godzilla, Kiryu, and Kumonga, but was joined by SpaceGodzilla. The space monsters defeated Kumonga and knocked Kiryu into submission, but SpaceGodzilla was frozen by a blast of Kiryu's Absolute Zero and subsequently defeated when Godzilla finished him with his atomic breath. With only Monster X and Godzilla still standing, Monster X transformed into his true form, Keizer Ghidorah. Keizer Ghidorah dominated his weakened and smaller opponent, tossing him into the sky and blasting him across New York City with his gravity beams.

The tables were soon turned when Godzilla's ally Rodan arrived and decapitated one of Keizer Ghidorah's heads with a sonic boom from his wings. Godzilla seized the opportunity and fought back against Keizer Ghidorah, severing another head with his atomic breath. With Keizer Ghidorah laying hopelessly maimed on the ground, Godzilla stomped on the creature's remaining head repeatedly, crushing his skull and killing Keizer Ghidorah.

Godzilla: Unleashed
Monster X/Keizer Ghidorah was briefly considered for the game Godzilla: Unleashed, but creator Simon Strange said that he "wasn't interesting enough" and it would be too complex to animate his transformation.

Godzilla: Kaiju Collection
Keizer Ghidorah makes his first video game appearance in the 2015 mobile game Godzilla: Kaiju Collection. Both his Monster X and Keizer Ghidorah forms are playable, and are two of the most powerful kaiju in the game.

Powers
As Monster X, he can fire gravity beams from his eyes and side skulls and levitate and has demonstrated the ability to withstand Godzilla's atomic blast at point blank range. As Keizer Ghidorah, he is even larger and stronger than he was as Monster X and possesses the same abilities as King Ghidorah, as well as an energy-draining bite. Though he possesses wings, it is unlikely he can fly very much and only uses them to crush enemies with his bulk. However in the comic series Godzilla: Rulers of Earth, Keizer Ghidorah is able to fly fairly competently.

Trivia

 * Keizer Ghidorah is the third Ghidorah to appear in a film, after King Ghidorah and Desghidorah.
 * In both his appearance in Godzilla: Final Wars and IDW's Godzilla comic series, Keizer Ghidorah acts as a Bigger Bad for another antagonist. In Final Wars, Keizer Ghidorah overtakes Gigan and X as the final villain in the film after the latter two are killed, and in IDW's Godzilla he is revealed to be the bigger threat after SpaceGodzilla is defeated.
 * Keizer Ghidorah is sometimes thought to be the main antagonist of the film. However, X is the true antagonist due to having created him and having bigger plans than anyone else. Despite this, Keizer Ghidorah is far more dangerous than X and after his death, Keizer Ghidorah becomes the leader and final main antagonist.
 * Keizer Ghidorah, King Ghidorah, Destoroyah and SpaceGodzilla are the only Godzilla Kaiju Villains to be considered Complete Monsters.
 * Keizer Ghidorah is the second tallest main series Godzilla monster, behind the Heisei King Ghidorah and Mecha-King Ghidorah.
 * Monster X's transformation into Keizer Ghidorah was kept secret by Toho prior to the release of Godzilla: Final Wars, in order to surprise fans. To further keep Keizer Ghidorah a secret, Toho trademarked it as "Monster X II" rather than under its true name.