Originating as a microscopic life-form from the Dark Gas Nebula in the Orion Constellation, the creature came to Earth inside a comet which fell in the Pacific ocean, near the coast of Japan; where it proceeded to multiply and form increasingly complex multi-celled structures; a superorganism, resulting from the combination of millions of individual beings working together. It seems to thrive on organic waste, increasing rapidly in size due to the pollution of the area it fell upon. Throughout its growth it morphs into different body types: multiple small tadpoles which could fuse together to a gigantic fish-like form; a terrestrial octopus like form; a flying saucer like form which flies by means of nuclear energy; and finally a 60 meters tall terrestrial form with a quasi-humanoid shape and huge red eyes.
Hedorah's internal fluids are highly corrosive, and can be sprayed on its opponents as an attack or defense mechanism. It is physically durable, can easily regenerate when cut, and suffers no effect from concentrated radiation, such as Godzilla's atomic ray. However, it is vulnerable to loss of water, needing a certain amount of moisture to live. On its flying form, Hedorah is able to spread deadly mists of sulfuric acid. On its final form, Hedorah is also able to fire red Crimson energy beams from its eyes. It can also separate its body to form two or more entities, and morph together with them at any moment. Its final form is able to quickly change back into its flying form, and presumably the other forms as well, if it wishes.