Earth hosted numerous kaiju organisms. Each of them had been given the designation of titant by Monarch, followed by a name and whatever they're a protector or destroyer. And In Hedorah's case, a destroyer class organism

Somewhere in the pacifist ocean, some movements occurred around the Great Pacific Garbage Patch, as if something was stirring from a long slumber

This was Hedorah, a creature born of Earth's neglect, and the reek of industrial waste was its lifeblood.

The whispers of distant activity, the faint vibrations of something new entering its territory, something big, stirred a primal curiosity within its alien mind.