Brock is described as being bored by no one being able to defeat him, or even get past the preliminaries. To gain access to Brock, a trainer must win several rounds of battles against special trainers of the gym, and all of those battles are watched by him from a special room.

Brock is a brave trainer, and he assists Erika and Misty in their battles against Team Rocket. 

The voice we are looking for in terms of Brock is something close to how Tom Bauer did Brock in Pokémon Masters EX: Brocks Voice reference