Gigan

Gigan is a gigantic alien cyborg employed by the Nebulons to overtake Earth.

History
Gigan was sent to Earth with the three-headed monster King Ghidorah to destroy Tokyo. Godzilla and Anguirus put up a fight, and after a long and grueling battle were forced to retreat. About a year later, Gigan was sent back to Earth to help the Seatopians destroy humanity. He fought alongside Megalon against Jet Jaguar and Godzilla. When the odds turned against them, Gigan abandoned Megalon, leaving him for dead. Later that year, he was sent back to Earth again to help the Garogas fight Godzilla and a giant superhero known as Zone Fighter. It was at this battle that Gigan finally met his demise by Zone Fighter's Meteor Missile Mite attack.

Gigan appeared later, revived by the Xiliens to take over Earth. He was sent to the South Pole to destroy a flying ship called the Gotengo. Instead, he wound up fighting Godzilla and was killed after his head was blown of by Godzilla's atomic breath.

Gigan later returned, resurrected again and upgraded with new abilities, such as chainsaws in place of scythes and the ability to fire razor discs from his chest. Interrupting a battle between a Godzilla-Mothra team and Monster X, he joined Monster X. He managed to cut off one of Mothra's wings, incapacitating her; he and Monster X then attacked Godzilla. Then, Mothra came back and attempted to kill Gigan. He fired two discs at her, but their targeting was disrupted by her scales. He then fired his laser at her, setting her on fire. Just as he thought he had finally triumphed over his ancient nemesis, the two discs that had missed Mothra came back and decapitated him. He remained alive, but then Mothra, covered in flames, flew down and hit Gigan, finally putting and end to the cyborg's reign of terror...although whether or not it was for good remains to be seen.

Abilities
Gigan's eye can generate a powerful laser that can easily cut through buildings. He also has scythe-like arms so sharp they can even cut Godzilla. He has a powerful and durable buzz saw going down his chest and stomach; it was sharp enough to rip open Godzilla and cause him to spurt blood. Gigan can fly as well - it is assumed that he uses anti-gravitational abilities to fly as his wings are far too stubby to carry his massive body.

Trivia

 * Gigan was the very first monster to ever cause Godzilla to visibly bleed. This can be witnessed in the movie Godzilla vs. Gigan.