- Voice actor: Unshō Ishizuka (both English and Japanese)
Onix resembles a giant chain of gray boulders, with a rocky spine on its head. This Pokémon has a magnet in its brain that serves as an internal compass. Onix's body becomes more rounded and smoother as it grows with age. A fully-grown Onix measures at an enormous 28 feet 10 inches, or 8.8 meters. Its height is 28'10" and weight is 463.0 lbs.
Onix can have the ability Rock Head or the ability Sturdy. Rock Head prevents Onix from recoiling. Sturdy gives Onix immunity to OHKO moves. Onix tunnel under the ground at over fifty miles per hour, which causes tremors. It has a compass in its brain that can tell what direction Onix is facing.
They are very hotheaded Pokémon and will constantly attack humans and Pokémon when various objects are caught in its craggy body. However, domesticated Onix will show signs of distress instead of attacking others.
Onix can be found in mountains and caves, though they prefer underground tunnels with little light. It can also be found in craggy mountains and abandoned mines.
- Main article: Pokémon food
Onix eats large boulders.
Onix's first major appearance was in Showdown in Pewter City under the ownership of Brock. He used it in his journeys in Kanto and Johto before giving it to his little brother, Forrest, in A Family That Battles Together Stays Together!. At some time before Grating Spaces, it evolved into a Steelix.
The Crystal Onix featured a special Onix whose body is made out of glass crystal. Ash and his friends helped a glass sculptor named Mateo search for it because Mateo believed it would help inspire him to be better at his craft.
In Hello, Pummelo!, Drake of the Orange Crew owns an Onix and he used it to fight Ash's Squirtle in the second round in the Orange League Champion match. During the battle with Squirtle, Drake's Onix dug underground and emerged to use Bind on Squirtle, but Squirtle used Withdraw followed by a Hydro Pump, soaking Drake's Onix into submission. After drenching Drake's Onix, Squirtle defeated the Onix with a Skull Bash. It reappeared in a flashback in the following episode.
A "King Onix" was featured in Hooked on Onix. Team Rocket tricked King Onix into thinking Ash and his friends were going to destroy his kingdom. When Ash managed to convince King Onix that he and his friends weren't bad by defeating it in a battle, Team Rocket tried to steal the royal Rock Snake Pokémon, but their plan was foiled, as usual.
Roark's Onix was first seen in Shapes of Things to Come where it was used against Paul's Elekid and Chimchar. In A Gruff Act to Follow!, it defeated Ash's Turtwig, followed by Ash's Pikachu but Pikachu managed to defeat it in a rematch in O'er the Rampardos we Watched!.
A rampaging Onix appeared in A Maze-ing Race!.
Multiple wild Onix are set to appear in BW087.
An Onix appeared in Mewtwo Strikes Back.
Multiple wild Onix appeared in To Master the Onixpected
Multiple Onix also appeared in The Power of One.
An Onix was seen in a fantasy in The Rivalry Revival.
An Onix, under the ownership of a trainer, appeared in Celebi: Voice of the Forest.
An Onix appeared in the opening of Destiny Deoxys.
Multiple Onix appeared in Lucario and the Mystery of Mew as part of the feuding armies.
An Onix made a brief cameo in Pokémon Mystery Dungeon: Explorers of Sky - Beyond Time & Darkness.
Brock used an Onix in One Team, Two Team, Red Team, Blue Team! as part of the Pokémon Triathlon.
An Onix appeared in A Rivalry to Gible On!.
An Onix appeared in the opening scenes of Zoroark: Master of Illusions.