Mechagodzilla

"You could call it a Mechagodzilla."

- Hideto Miyajima in Godzilla vs. Mechagodzilla

 (メカゴジラ, Mekagojira) is a robotic monster created by the Black Hole Planet 3 Aliens, the secondary antagonist of the Godzilla series behind King Ghidorah and the titular main antagonist of the last Showa Godzilla films, Godzilla vs. Mechagodzilla and Terror of Mechagodzilla.

Appearance
Mechagodzilla is a robot that resembles Godzilla from the 1970's.

The original Mechagodzilla in Godzilla vs. Mechagodzilla has shorter finger missiles, a metal piece with three bolts on the hand plate, a less defined and prominent shoulder frill, one orange button each on the chest and above the crotch, a square underneath the chest laser, two circular markings coming from the chest canon, a smooth and solid tail blade, and red "MG" initials on its arms that stands for "Mecha Godzilla".

The rebuilt Mechagodzilla from Terror of Mechagodzilla has longer finger missiles, one big metal piece on its hand plate, a more defined and prominent shoulder frill, one silver button on the chest, one silver button underneath the chest cannon and two silver buttons above the crotch, an upside down triangle underneath the chest laser, two lightning-like markings coming up the chest, a smooth and solid tail blade with three big bolts in it, and blue and orange "MG2" initials on its arms that stands for "Mecha Godzilla 2", thus giving it the name   (メカゴジラ2, Mekagojira Tsu).

Godzilla vs. Mechagodzilla
Mechagodzilla launched an assault on the Earth in a Godzilla disguise of pseudo flesh covering. Anguirus wasn't fooled by this masquerade and attacked Mechagodzilla. However the kaiju was defeated and forced to flee after having his lower jaw snapped. However the fight did tip off the humans to Mechagodzilla's farce after Anguirus scraped off part of his disguise and exposed the metal underneath. Eventually Godzilla arrived to challenge his doppelganger and blasted off the rest of Mechagodzilla's disguise with his atomic fire breath. The bionic monster then unleashed his full abilities on Godzilla, easily overwhelming his organic counterpart, but was called back for repairs due to damage the King of the Monsters had inflicted on him. Mechagodzilla was sent back into action after its creators found the location of the guardian kaiju, King Caesar. They hoped to destroy him before he could awaken and stop their plans, but Mechagodzilla failed to do so. The bionic monster engaged King Caesar and initially had trouble fighting him, due to the guardian kaiju's ability to reflect the robot's eye beams, but was eventually beaten senseless by Mechagodzilla. Godzilla joined the fight to try and turn the tide, only for the robotic terror to let loose its whole arsenal on its two opponents. However the King of the Monsters generated a magnetic field around himself (it isn't explained how this was possible, but it may have been due to the lightning bolts that struck him earlier in the movie). Mechagodzilla tried to fly away from Godzilla, but the field was too strong and pulled in the bionic monster. The King of the Monsters managed to take hold of the robotic terror and twisted off his head (which is strange considering the fact that it demonstrated the ability to easily spin its head around earlier). Mechagodzilla exploded, scattering its remains into the ocean.

Terror of Mechagodzilla
While Mechagodzilla was defeated in the previous film, the Simians weren't finished yet. The Simians rebuilt their machine titan and, after seeing the power of teamwork, called in an old debt to team Mechagodzilla with Titanosaurus. The aquatic dinosaur first tried to fight Godzilla alone, but was defeated while Mafune, a mad scientist, began rebuilding Mechagodzilla. He believed that the bionic monster would allow him to bring about his revenge on his own species, man, for all the other biologists thinking he was crazy. Mafune believed that he wouldn't have to obey the aliens since he thought that Titanosaurus would fight Mechagodzilla and emerge victorious due to the dinosaur having an organic brain, thus giving it an advantage over the machine. The aliens promised Mafune that they would build a new home for him and his daughter, Katsura, from the ruins of Tokyo with highly advanced technology. However she was rebuilt as a cyborg in control of the two monsters by the aliens and Mechagodzilla and Titanosaurus engaged Godzilla. The King of the Monsters attempted to tear off the robotic terror's head to defeat it again, but the bionic monster was able to continue to fight. However Katsura let herself die so as to stop Mechagodzilla and with her gone, the robotic terror was unable to move. Godzilla destroyed the bionic monster with his atomic breath and Titanosaurus was soon defeated as well.

Godzilla Island
An incarnation of this villainous MechaGodzilla also featured in TV Series titled Godzilla Island, where just like in Godzilla vs. Mechagodzilla, it disguised as Godzilla with pseudo flesh covering to frame him for destruction across Japan that real Godzilla didn't do. This fake Godzilla, whom mistaken by protagonists (namely G-Guard Commander and Torema) as real Godzilla, eventually able to capture it and incarcerated it in the cave like a prison. The fake Godzilla however, managed to escape after Rodan, Mothra, Moguera, and Super Mechagodzilla distracted by Battra and Megalon's attack on Godzilla Island and resume the rampage.

Still believing that fake Godzilla is the real Godzilla that somehow turned evil, Torema tried to reasoned with it, only to be attacked. When the hope seemed lost, the real Godzilla showed up and saved her. Much like in Godzilla vs. Mechagodzilla, Godzilla exposed his doppelganger's true identity by burned its pseudo flesh covering with his signature atomic breath and destroyed the robotic terror, ending it's rampage and clear his name in process.

Godzilla: Legends
Several under-construction Mechagodzillas appear at the end of issue #3 of the comic miniseries Godzilla: Legends. It is revealed that the Simians plan to use them along with the mind-controlled Titanosaurus to invade the Earth before their homeworld is destroyed.

Godzilla: Rulers of Earth
An army of Mechagodzillas appears in the comic series Godzilla: Rulers of Earth. In order to get revenge on Godzilla and conquer the Earth for his race, the leader of the Cryog aliens, Rhizon, posed as a Russian warmonger named Dyachenko and constructed an army of Mechagodzillas, then sold them to the various governments of the world, who would use them to destroy Earth's kaiju, playing right into Rhizon's hands. When Godzilla suddenly appeared in Boston, Rhizon received permission to unleash his Mechagodzillas against him. Godzilla survived the Mechagodzilla onslaught, but was captured by Rhizon's other robot, Mecha-King Ghidorah and taken to the Dyachenko Robotics facility in Russia. Godzilla was attacked by serveral more Mechagodzillas there, but was aided by the monster Anguirus. Together, Godzilla and Anguirus forced Mecha-King Ghidorah to retreat and destroyed all but two of the Mechagodzillas.

Rhizon later retreated with the Mechagodzillas to his ship in outer space, where he found himself under attack by SpaceGodzilla. Rhizon deployed the two remaining Mechagodzillas to fight SpaceGodzilla, but they were frozen in the vacuum of space, allowing SpaceGodzilla to easily destroy them.

Abilities
Mechagodzilla possesses enormous strength and is made of "Space Titanium." It is equipped with an enormous arsenal, including eyebeams, an energy beam fired from its chest, and missiles on its fingers, knees, and toes, which can also funciton like darts. Mechagodzilla can also spin its head around to generate a powerful shield and fly at mach 5.

Trivia

 * While the rebuilt version of the Showa Mechagodzilla is officially called "Mechagodzilla 2," the name "Mechagodzilla 2" is also sometimes used to refer to the Heisei Mechagodzilla, due to the fact that the official international title of its debut film was Godzilla vs. Mechagodzilla , and that the Heisei version of Mechagodzilla was the second distinct incarnation of the character. The Heisei Mechagodzilla is, however, never referred to by the name "Mechagodzilla " in the film due to being the first and only Mechagodzilla within the Heisei continuity.
 * In the comic series Godzilla: Rulers of Earth, where there is an entire army of Mechagodzillas, each one is labeled with a different number emblazoned under the "MG" on its arm.
 * The later incarnations of Mechagodzilla that followed after Terror of Mechagodzilla were human-built and portrayed in a more heroic light, though the evil original incarnation of Mechagodzilla continued to appear in non-film media, even battling the later incarnations of Mechagodzilla in some media.
 * WatchMojo.com listed MechaGodzilla as #2 on their "Top 10 Godzilla Villains" list.