The Rhedosaurus is a giant carnivorous man-eating monster lizard/giant dinosaur and the main antagonist of the 1953 film The Beast From 20,000 Fathoms.
The Rhedosaurus is a 200-foot long carnivorous dinosaur that was frozen in ice in the Arctic during the Ice Age, where it had been held in suspended animation for millions of years. The last surviving member of its species, it was only released from its hibernated state when it was thawed by an atomic bomb test in the Arctic Circle. Making its way alongside the East Coast of North America towards its original home, where New York City is located, the Rhedosaurus destroys everything that stands in its path.
It sinks a fishing ketch off the Grand Banks, destroys another near Marquette, Canada, wrecks a lighthouse in Maine, and destroys buildings in Massachusetts. Its enemies, the soldiers who attempted to kill it were complicated, because of the ancient disease it carried; spilling its blood that can make people sick and die with an ill feeling while the plague from its blood has freed, which was almost as deadly as a dangerous venomous creature itself. It bleeds all over the streets of New York, unleashing a horrible, virulent prehistoric contagion, which begins to infect the populace, causing even more fatalities. The infection precludes blowing it up or even setting it ablaze, lest the contagion spread further. It is then decided to shoot a radioactive isotope into the Rhedosaurus' neck wound with hopes of burning it from the inside, killing it without releasing the contagion.
When it comes ashore and reaches Coney Island's amusement park, military sharpshooter Corporal Stone takes a rifle grenade loaded with a potent radioactive isotope and climbs on board a roller coaster. Riding the roller coaster to the top of the tracks to get eye-level with the beast, he fires the isotope into its open neck wound. The beast thrashes about in pain, causing the roller coaster to spark when it collapses to the ground, setting the amusement park completely ablaze. Letting out one last roar, the Rhedosaurus perishes from the poisoning and heat.
- The scene where the Rhedosaurus destroys a lighthouse was based on the short story The Fog Horn.
- The Rhedosaurus was one of the main inspirations for Godzilla, along with King Kong.
- The Rhedosaurus puppet was used again in the film Planet of the Dinosaurs, where it played another Rhedosaurus who was doomed to be killed by a Tyrannosaurus rex.
- The Rhedosaurus makes a cameo appearance in the 6th episode of the 2nd Season of ABC's Whose Line Is It Anyway?.