Throughout the decades, Godzilla has encountered and fought many monsters with all sorts of unique origins, from mutated prehistoric creatures like him, to cutting-edge machines built solely to destroy him. But there’s also another prevalent category of antagonists in this series, and that is alien monsters.

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Almost every era of the Godzilla franchise is graced with the presence of one or more kaiju from outer space that want to defeat the King of the Monsters in order to conquer Earth. Their extraterrestrial background means that they can often have really distinctive and memorable designs, personalities and power sets. This is the definitive ranking of every alien monster that Godzilla has encountered in his films.

7 Hedorah

A Parasite Who Feeds On Pollution

Godzilla Vs Hedorah:

• Released: July 24, 1971
• Era: Showa
• Studio: Toho Pictures
• Director: Yoshimitsu Banno

First introduced in 1971’s Godzilla vs. Hedorah, this is one of the strangest yet most unforgettable monsters in the entire franchise. Hedorah was born as an unknown alien life form who arrived on Earth alongside a comet and immediately grew in size by feeding on humanity’s pollution. So this monster was created around an explicit anti-pollution message that was as relevant in 1971 as it is today.

On top of that, Hedorah proved to be a powerful foe that, due to its resilient body and toxic sludge, managed to give Godzilla a tough fight, even if its design left a lot to be desired. While its original appearance was very memorable, its brief cameo in Godzilla: Final Wars was pretty disappointing. In fact, Hedorah deserves its own modern movie to redeem that appearance.

6 Monster X/Keizer Ghidorah

A Terrifying New Twist On An Old Classic

Godzilla: Final Wars

• Released: December 4, 2004
• Era: Milennium
• Studio: Toho Pictures
• Director: Ryuhei Kitamura

Godzilla: Final Wars was a true celebration of the franchise, with Godzilla fighting many of his classic enemies throughout the film, all of which were being controlled by the alien race known as the Xiliens. The final boss of this ordeal had to be a truly intimidating and powerful monster. This was the role of Monster X, a humanoid kaiju with an interesting skeletal design that helped it stand out from the other aliens in the series.

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Monster X was surprisingly strong, as it could stand toe-to-toe against Godzilla himself. But the most memorable aspect about this kaiju was its unexpected transformation into Keizer Ghidorah, a quadruped incarnation of the classic villain who was far more powerful than anything else in this movie. The final encounter between Godzilla and Keizer Ghidorah was incredible, and the best way to celebrate Godzilla’s 50th Anniversary.

5 Orga

An Entire Alien Civilization Living On As A Godzilla Clone

Godzilla 2000: Millennium

• Released: December 11, 1999
• Era: Millennium
• Studio: Toho Pictures
• Director: Takao Okawara

Orga is not the typical alien monster, as it is instead an entirely different and more abstract being. When an alien species known as the Milennians absorbed Godzilla’s DNA, they, alongside the spaceship they were residing in, mutated into this monstrous clone of the King of the Monsters, which is a truly mind-blowing concept for a kaiju.

While there’s no shortage of Godzilla doppelgängers in the franchise, Orga stands out because it’s actually a failed clone with a grotesque appearance. It also has incredible physical strength and even a destructive shoulder cannon that it inherited from its U.F.O form. Orga is a truly unique alien for this series, and it will always be remembered for its violent death, when Godzilla unleashed a devastating nuclear pulse while the clone was trying to devour him.

4 Mechagodzilla

The Original Mechanical Doppelgänger

Godzilla Vs Mechagodzilla:

• Released: March 21, 1974
• Era: Showa
• Studio: Toho Pictures
• Director: Jun Fukuda

While most audiences nowadays are familiar with Mechagodzillaas a human-made weapon built to defeat Godzilla, this robot was actually made by an alien race in its first ever incarnation. In the original Godzilla vs. Mechagodzilla, the Black Hole Planet 3 Aliens built this machine and disguised it as Godzilla in order to destroy the Earth.

When the real Godzilla appeared and defeated this impostor, it revealed itself as Mechagodzilla. Because of its extraterrestrial origins, the first iteration of this character felt more evil and violent than anything that came after, which was reflected in the wild battles it had against Godzilla. Its intimidating design also feels otherworldly, and it’s just a really solid kaiju that set the foundation for many other great mechanical doppelgängers in the ensuing years.

3 Gigan

A Ruthless Cyborg Chicken From Space

Godzilla Vs Gigan:

• Released: March 12, 1972
• Era: Showa
• Studio: Toho Pictures
• Director: Jun Fukuda

During the Showa Era, Toho specialized in creating some of the most bizarre and unique monster designs in all of cinema. The kaiju that best reflects their design philosophy was none other than Gigan, introduced in his very own movie. This is a giant bird-like monster with scythes for hands, a buzz saw in its stomach, and a visor for an eye. It used all of these features to its advantage in order to deal some serious damage to Godzilla, to the point that it even made him visibly bleed.

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The original Gigan that appeared in Godzilla vs. Gigan and Godzilla vs. Megalon was already extremely charismatic, but his reappearance in Godzilla: Final Wars cemented him as one of the most popular monsters in the entire franchise, and for good reason. This time, Gigan was redesigned with a black & red color scheme and a grappling hook in his claws. It even got an upgrade again later in the film, when his scythes were replaced with chainsaws. Gigan is a great alien monster that could only exist in a franchise as crazy as Godzilla.

2 SpaceGodzilla

The Most Powerful And Threatening Godzilla Clone

Godzilla Vs SpaceGodzilla:

• Released: December 10, 1994
• Era: Heisei
• Studio: Toho Pictures
• Director: Kensho Yamashita

Godzilla vs. SpaceGodzilla answers the question: What would happen if Godzilla’s cells fell into a black hole? The result would be SpaceGodzilla, known among Godzilla fans as one of the most powerful and evil giant monsters ever put on film. While he obviously looks like the King of the Monsters, and shares most of his physical attributes, this alien kaiju’s power set is completely different.

SpaceGodzilla’s main gimmick is his ability to generate and control massive crystals that he can use for both offensive and defensive means. On top of that, he can also fire a powerful energy beam and use telekinesis to move objects around. This is a true space beast that used his powers to kidnap Little Godzilla and create his own fortress in Fukuoka, only to be eventually killed by Godzilla in an epic final showdown. Nevertheless, SpaceGodzilla is a popular character who should definitely reappear in a future installment someday.

1 King Ghidorah

Godzilla’s Arch Nemesis Comes From Outer Space

Godzilla: King Of The Monsters:

• Released: May 31, 2019
• Era: Monsterverse
• Studio: Legendary Pictures
• Director: Michael Dougherty

King Ghidorah is well known for being Godzilla’s longest running and most famous monster enemy. While he’s not an alien in all of his appearances, this is a character who works way better when he’s a legendary being from outer space that is determined to destroy Earth, especially when he acts on his own accord, and he is not being controlled by some other alien race.

The original King Ghidorah from the Showa Era was such a big threat that it took the efforts of several monsters to defeat him. Even his incarnation from the Rebirth of Mothra trilogy was a powerful monster, and those movies brought back his extraterrestrial background. Even Void Ghidorah from Godzilla: The Planet Eater was a unique take on the character that was inspired by eldritch Lovecraftian horrors from other dimensions.

Yet the King Ghidorah from the modern Monsterverse is possibly his most memorable version, where he’s established as an alien life form who invaded Earth millions of years ago and has an ancient rivalry with Godzilla. Coupled with the fact that all of his incarnations featured amazing original designs and some mind-blowing & effective powers, and there’s no question that King Ghidorah deserves his reputation as the most memorable alien monster in the entire Godzilla series.

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