M.U.T.O.

The Massive Unidentified Terrestrial Organisms, more commonly and simply referred to as M.U.T.O.s are the sole primary antagonists of the 2014 60th Anniversary Godzilla reboot movie, Godzilla. The Female M.U.T.O. is the true main antagonist, while the Male M.U.T.O. is the direct secondary antagonist. This said, they are both ultimately anti-villains, as they are not malicious organisms and are burdened solely with the survival of their species.

They are giant prehistoric parasitic creatures of unexplained origin and are ancient parasites that come from the same era and ecosystem as Godzilla. Much like him, the M.U.T.O. feed off of radiation. However, unlike the surviving Godzilla, who adapted to live at the bottom of the ocean and feed off the planet's natural radiation, the M.U.T.O. are actively drawn to sources of man-made radiation such as nuclear warheads and chemical weaponry.

History
The M.U.T.O.s were discovered in the Philippines in 1999 after a mining operation drilled into a cave containing two pods containing the M.U.T.O.s, one of which had already hatched. The newly hatched male M.U.T.O, who had hatched after being disturbed by the cave collapsing, burrowed its way to the Janjira nuclear power plant in Japan, where it caused the plant to collapse from underneath, killing Sandra Brody and several other workers, and causing the entire are to be evacuated because of radiation leaking from the plant.

This was the work of the recently hatched male M.U.T.O., who was looking for a source of radiation that would be able to grow and sustain it while it entered hibernation. Despite the destruction of the plant, the M.U.T.O. linked itself to the radiation hot spot and entered a cocoon-like state, absorbing all the radiation from the surrounding area. The second pod containing the female M.U.T.O was taken by the Americans to the Yucca Mountain Nuclear Waste Depository in Nevada.

15 years later, the male M.U.T.O. finally emerges from its cocoon and lets out a mating cry for its female counterpart. It lays waste to the power plant once again before sprouting its wings and taking off. It later appears in Hawaii, where it faces Godzilla but flees after a short battle. Meanwhile, the female M.U.T.O. hatches as well and breaks out of the mountain it was contained in, and begins to make its way through Las Vegas, Nevada.

Both the winged and eight-legged M.U.T.O. arrive to fight Godzilla in San Francisco, California, after the M.U.T.O.s were lured there with a nuclear bomb, and Godzilla, in turn, was lured there by the M.U.T.O.s. In the following hours, after setting up their nest and using the bomb to feed their eggs, both M.U.T.O.s are able to overpower and mercilessly pummel Godzilla. Ford Brody manages to destroy the M.U.T.O. eggs, which draws the rage of the female M.U.T.O. onto him and away from Godzilla. Godzilla then rises back up and attacks the female with his atomic breath, but before he can finish her off, the male attacks Godzilla once more. The two battle until Godzilla kills the male by smashing it into a building and impaling it, but by then, the female had already fled to chase after the bomb.

Ford's team is slaughtered by the M.U.T.O., leaving Ford alone to try and get the bomb out to sea where it can explode safely. Despite this, the M.U.T.O. is easily able to catch up, both seeking a new source of radiation and knowing Brody was the one that destroyed her nest. Before she can destroy the boat and kill Brody though, Godzilla re-emerges and kills the eight-legged M.U.T.O. by holding her mouth open and firing his atomic breath into her throat, causing her neck to explode, Godzilla to let her head fall into the water, and falls onto some destroyed buildings, exhausted, before regaining enough strength to return to sea.

Trivia

 * Originally, Godzilla's opponents in the film were intended to be a six-legged ankylosaurus-like monster called Rokmutul and a pterosaur-like creature called Pterodactyl. Both monsters closely resembled the classic Godzilla monsters Anguirus and Rodan, and were most likely designed as stand-ins for them. A different concept monster appeared in the original Comic-Con teaser trailer for the film. This monster, nicknamed "Vishnu" by fans, only appeared briefly laying dead, and looked like a giant tardigrade.