Brock

Brock is a Rock type specialist and the gym leader of Pewter City. His starter Pokemon is an Onix.

History
Brock is the Pewter City gym leader. The first time Daryon's travelling group meets him, they challenge him to a gym battle. After an interruption by Brock's younger brother Forrest, Brock puts a rain check on the challenge before going to handle a situation with Team Rocket. He is overpowered by the Team Rocket grunts, but is able to defeat them with the help of Daryon, Evan, and Cameron.

Brock is defeated during Cameron's gym battle due to a strategic use of String Shot and Poison Stings. Brock quickly knocks out all of Daryon's Pokemon, followed by all of Skye's Pokemon, before losing to Daryon's Nidoran and Bulbasaur during Daryon's rematch. He is shown to be a fair sport and doesn't show any negative response to losing.

Onix.
Onix is Brock's first and strongest Pokemon, measuring in at over 28 feet.

Geodude.
While Onix is Brock's starter Pokemon, for some reason or another Brock seems to use his Geodude more often. Geodude is capable of taking down enemies in a single blow using Rock Throw.

Trivia

 * All of Brock's Pokemon, in addition to being Rock type, are also Ground type.