Godzilla's originated as a dinosaur known as the Godzillasaurus. The dinosaur was mutated by nuclear radiation and became a giant, multi-ton gargantuan beast. The creature had a murderous hatred against humanity for mutating him and went on a rampage across Japan, killing thousands. A scientist named Daisuke Serizawa built a device known as the Oxygen-Destroyer that asphyxiates the victim, destroys oxygen atoms, and disintegrates the victim. The device was used on the monster, and the creature died, but Serizawa committed suicide to keep the military from using the weapon for war.
Unfortunately, Godzilla was just one member of a species of mutated Godzillasauruses. A second Godzilla rose to wreak havoc and fought another mutated dinosaur, this time a mutant ankylosaurus named Anguirus. After Anguirus was defeated, Godzilla was overwhelmed and buried in an avalache. Godzilla wasn't finished, yet. Several years later Godzilla was able to escape and fought another iconic monster, a giant ape King Kong. Godzilla overwhelmed Kong, who was forced to retreat and was captured by the Japanese. The Japanese decided to use Kong to fight Godzilla again, in the hopes of them killing each other. Godzilla climbed up a mountain and Kong was lifted to Godzilla via helicopter. Godzilla and Kong saw each other and Kong was released, and he tackled the King of the Monsters, and a brawl started. Godzilla initially had the upper hand, using his atomic breath to weaken Kong and battered him with his superior strength. Kong was briefly defeated, but was revived by a lightning storm. Kong got up and was able to gain the upper hand in his fight with Godzilla, and they eventually fell off a cliff and into the sea. Kong swam away from Godzilla, who remained underwater, with bystanders wondeirng if Godzilla survived.