Brock is the first Gym Leader in the whole Pokemon series. After getting your first pokemon, and learning some basics he's not far away. During my play-through of Pokemon Blue he was able to beat since Squirtle easily over-powered the rock-type Onix and Geodude. I did love playing against him again during Pokemon Silver when the new Pokemon trainer leaves his native Johto region and enters the original Kanto.
I have to admit while playing Pokemon Yellow (which requires your starter pokemon to be Pikachu) the fight against Brock felt just like the anime battle. PAINFUL.
After being a jerk in the anime, he then becomes an lovable oddball idiot.