Hedorah was a giant monster.
Also known as the Smog Monster. Hedorah was spawned from the combination of an alien mineral and toxic wastes dumped into the ocean. 'His' name was coined by Dr. Toru Yano's son, Ken. The creature began as many tadpole-like creatures, which eventually combined into one giant frog-like creature. Later, it metamorphosed into a flying manta ray-like form, which left a trail of sulfuric acid mist as 'exhaust.'
Its final form was a humanoid. Hedorah could not only blast toxic chemicals and gases at its enemies, but also fire eyebeams. Godzilla fought the monster, but was unable to harm it- the military was forced to assist by dehydrating the creature, which was its only weakness.