Hedorah

Hedorah, also known as the Smog Monster, is an alien that feeds on pollution and is one of Godzilla's most powerful enemies. He first appeared in Godzilla vs. Hedorah, which is also his most famous appearance.

Godzilla vs. Hedorah
In the outer regions of space, a microscopic alien lifeform attaches itself to a comet and when it bypasses Earth, the alien falls to the planet. A fisherman named Gohei finds the creature while trying to catch shrimp and assumes it is a new species of shrimp and he gives it to a scientist named Professor Yano to study it. His studying is cut short when a giant creature resembling the smaller alien attacks two ships and sinks them both. Yano investigates the nearby bay to search for the creature while his son Ken waits for him. While Yano is gone, the giant alien attacks Ken, who fights back with a knife. The creature is unaffected by Ken's attacks and instead leaves and attacks Yano, horribly deforming his face. The scientist returns home to nurse his injuries and further studies to smaller alien, and is able to find out that the creature can survive as long as it is moist and is able to feed on pollution. Yano also discovers that the alien, when cut in half, will not only survive, but both halves will grow into a larger creature. Ken speculates that the bigger creature, dubbed Hedorah, was able to grow faster because it fed on more pollution.

The larger Hedorah evolveed into a four-legged creature that moved onto land to feed on more pollution.