Brock's Steelix

This Steelix is a /-type Pokémon owned by Brock.

Original series
Onix was given to Brock by his father, Flint, on his 10th birthday.

It first appeared as an Onix in Showdown in Pewter City, where Brock used it to battle Ash's Pikachu. Because it was part ground-type, it was unaffected by Pikachu's electric attacks. However, after it was dowsed with water, Pikachu was able to affect it with its electric attacks, and ultimately knock it out.

When Brock joins with Ash and Misty from their travels, Onix is also used in some occasions, such as stopping Team Rocket for stealing the large Moon crater using Dig, entering a Pokémon-nathon race but it ends up disqualified because of its dislike of water, and Onix cries towards its trainer.

Later in Volcanic Panic Onix and Geodude are aiding Ash's Charizard and Pikachu and Blaine's Magmar to stop the lava flow that destroys Blaine's gym.

In Johto from the episode Sick Daze, Brock ends up getting sick and it forces Ash and Misty to deal with his note chores such as food and polishing rock Pokémon. After realizing how hard to polish them, Ash decides to use Totodile to washed them as Misty scolds him that rock Pokemon hates water which Onix was seen panicking and dodges to avoid its Water Gun. Later, Onix and the other Pokémon are captured by Team Rocket before Brock's Golbat manages to slice the Meowth Balloon with its Wing Attack. Onix uses Rock Throw on Team Rocket before being blasted off by Pikachu's Thunder.

In Great Bowls of Fire! during Dragonite's rampage at the Dragon Holy Land, Brock releases both Onix and Geodude as the latter to pull off its Rock Throw in order to stop the fire while Geodude rescues other Pokémon from being trapped.

Advanced Generation series
In Pokémon Chronicles from the episode, A Family that Battles Together Stays Together! While still an Onix, Brock uses it to fight his ditzy mother, Lola who is responsible for redecorate the Pewter Gym into an aquarium filled with her water Pokémon in order to put the gym back to its former glory. Onix fights Lola's Mantine and it uses Dig to remove the water from the field and attacks Mantine underneath. It got hit from Mantine's BubbleBeam before Onix grips it with Bind and defeats it with Slam when it attacks continuously from its BubbleBeam. Later, Brock lent it to his younger brother, Forrest, the next Gym Leader of Pewter City Gym to take care of it along with his other Pokémon before he left to Hoenn to meet up with Ash, May and Max.

When Brock returned to Pewter City in the episode Grating Spaces!, he discovered that his Onix had evolved into Steelix as he grips his trainer as a reunion and Brock recognizes it and became mostly pleased to his younger brother, Forrest for taking care of his Pokémon and letting his Onix to evolve. He also uses it to team up with Ash's Donphan against the gym remodelers which is Jessie and James in disguise and using two of Butch and Cassidy's Pokémon, Charizard and Aggron against them. After Team Rocket is revealed to be responsible for remodeling the gym and Meowth's attempt on stealing the Gym's Pokémon, Ash, Brock and Forrest manage to blast them off with a combination of Pikachu's Thunderbolt, Donphan's Hyper Beam, Steelix's Dragon Breath and Geodude's Sandstorm. After the incident, Brock continues his travel with Ash, May and Max and gives farewell to his family and his Pokémon.

Diamond and Pearl series
During Ash's first Gym battle against Roark who also owns both Geodude and Onix. Brock mentions of his own Onix who is now evolved into a Steelix and remarking of how Roark raises his own Onix. This also happens in Dealing with Defensive Types! when Brock was surprised to see Byron's Steelix also gains a Screech ability when it uses to lower more of Ash's Buizel's defense before it quickly defeats it. He also remarks that this ability is also shared from Roark's Onix knowing of their family bloodline while raising both of their Pokémon.

Voice actor
Unshō Ishizuka (Japanese and English)

Gallery
Steelix Brocka