Hedorah is an extraterrestrial kaiju formed from pollution that could feed on pollution. Falling to Earth as a cloud of spores, Hedorah hatched into millions of microscopic tadpole-like organisms which began to feed upon the toxins with which mankind had poisoned its air and water. As they increased in number and power, they began to merge into a giant monster of living sludge capable of reducing the entire planet to an uninhabitable wasteland.
Hedorah's transformations and composite physiology are thought to be the inspiration for the Heisei monster Destoroyah. Surprisingly, Hedorah has become one of the most famous Godzilla monsters.
At the time of his creation, he was without a doubt, alongside King Ghidorah, Godzilla's most challenging enemy. In the course of their fights, the King of the Monsters was continuously injured and found it very difficult to defeat him. Hedorah, with King Ghidorah, Mechagodzilla, SpaceGodzilla and Destoroyah, are considered to be some of Godzilla's most powerful enemies. Although in Final Wars, Godzilla defeated Hedorah with ease, he is still considered to be a powerful enemy of Godzilla simply because of the fact that he was at the wrong place at the wrong time.
Hedorah possesses many special abilities. As a composite kaiju formed from millions of smaller organisms, Hedorah is capable of assuming a number of different shapes to suit the particular situation. For traveling through water, Hedorah transformed into a giant tadpole monster similar to the base organism that composed it. For traveling on land, Hedorah became a four-legged pile of slime resembling a gigantic salamander and it also could assume a saucer-like shape which granted it flight capabilities. After being driven back by Godzilla several times, Hedorah assumed a gigantic humanoid shape that even dwarfed the king of the monsters. Thanks to the protean nature of its body, ordinary weapons passed right through Hedorah while even Godzilla's atomic ray was unable to inflict any lasting harm. Finally, since Hedorah fed on pollution, so long as a piece of it remained alive then Hedorah could retreat to absorb more pollution in order to regenerate itself.
Hedorah's primary form of attack was by spurting globs of its own corrosive sludge at its opponent. The slime was so acidic it was even capable of scarring Godzilla's usually impenetrable hide. It was also able to project crimson energy beams from its eyes while its flying form created a byproduct of sulphuric acid mist that melted any living creature that came in contact with it down to its skeletal frame just like the Oxygen Destroyer.
Hedorah was an alien life form that landed on Earth and began feeding on pollution. Hedorah's actions soon gained the attention of Godzilla, who attacked the Smog Monster as he was feeding off of a smokestack. At the time, Hedorah was still in a young form, and was easily trounced by Godzilla. The two creatures had a series of battles across Japan, and Hedorah continued to grow bigger and stronger, and achieved a flying saucer-like form, allowing him to fly and spread sulfuric acid mist across Japan while destroying many factories. Hedorah and Godzilla had a final showdown near Mt. Fuji, in which Hedorah achieved his final form, a bipedal, humanoid pile of sludge. Thanks to his acidic, poisonous body, as well as his lethal eye bolts, Hedorah very nearly put an end to Godzilla in their struggle. However, mankind had built a pair of gigantic electrodes near the warring kaiju with the intention of creating a superheated zone that would dry Hedorah out. During a period of the fight where Godzilla was knocked out, Hedorah was lured between the electrodes. Unfortunately, a fuse was blown, and the electrodes were useless.
Thankfully, Godzilla quickly came to the rescue again, using his breath to re-energize the electrodes. Badly dehydrated by their electricity, Hedorah tried to escape when in the film's most famous moment, Godzilla used his atomic ray as a jet to propel himself through the air after the sludge monster whereupon he returned Hedorah to the electrodes to be dried out completely. Sensing still wet sludge within Hedorah's husk, Godzilla proceeded to rip out Hedorah's innards and then used the electrodes to finally slay the last remnants of the polluted monster.
In Godzilla: Final Wars, Hedorah, along with Ebirah, is seen being blasted out of Tokyo Harbor by Godzilla and crashing into a building, with one of Ebirah's claws piercing one of Hedorah's eyes. The Smog Monster and the Sea Monster are then knocked out by a blast of Godzilla's atomic ray.
Hedorah appears as a villain in the 1988 NES game Godzilla: Monster of the Monsters, as well as the sequel, War of the Monsters. Hedorah was also an enemy in the Godzilla Game Boy title, in which it, along with King Ghidorah, was the only monster unaffected by Godzilla's blows.
Hedorah also makes a cameo appearance in the video game Godzilla: Destroy All Monsters Melee, where it randomly appears in disc form and slows the energy recovery. It can be killed, though this is difficult.
Hedorah is a boss in Godzilla Unleashed: Double Smash.
Hedorah is one of the title antagonists of the 1996 children's book Godzilla vs. Gigan and the Smog Monster, written by Alice Alfonsi, and published by Random House. The book's plot concerns Hedorah and Gigan's assault on Los Angeles, until both are challenged and ultimately defeated by the heroic Godzilla and Rodan.
Godzilla At World's End, a 1998 young adult novel by Marc Cerasini, and also published by Random House, features Hedorah among a global army of artificially created monsters; all sent forth by the mysterious crystalline beings dubbed The Ancient Ones, in order to eradicate mankind from the Earth.
The television series Godzilla Island featured Hedorah in several episodes, along with a related, but otherwise original character named Neo-Heodrah; a brightly colored blue and pink 'clone' that could spawn mutant mushrooms in mass, to infest the title island, and thus overwhelming the show's heroes.
Hedorah is the name of a British indie guitar band from Reading (UK).
Hedorah made an appearance in the IDW comic book series Godzilla: Kingdom of the Monsters in the 10th issue
Hedorah makes several appearances in the webcomic Bob the Angry Flower, most recently as a member of Bob's peculiar legal team.
Hedorah appears as part of Gary Panter's cover art for the album cover of Frank Zappa's 1978 LP record, Sleep Dirt.
Hedorah is set to appear in the fourth issue of the comic book miniseries Godzilla Legends.