Brock's Marshtomp is a Pokemon obtained by Brock in the Hoenn region.
Marshtomp was first seen as a Mudkip looking after baby Mudkip. He didn't trust Brock at first and often ran away from him. But when Brock risked his life to save him and a baby Mudkip, Brock gained his trust. Team Rocket attempted to steal the baby Mudkip and Meowth suggested that they steal Brock's Mudkip and Lotad as a super prize for the boss. But Brock protected them and they worked together to send Team Rocket blasting off and saved the baby Mudkip. In another episode, Team Rocket stole Ash's Pikachu, and Meowth asked why they didn't grab Brock's Mudkip. In another episode, Team Rocket attempted to steal everybody's Pokemon including Brock's Mudkip, but they were rescued by their trainers. In another episode, Team Rocket made another attempt at stealing everybody's Pokemon including Brock's Mudkip. In one of the Battle Frontier episodes, Mudkip evolved into Marshtomp. Marshtomp was confirmed male when he was seen having the same personality as his trainer falling in love with girls. In another one of the Battle Frontier episodes, Team Rocket attempted to steal Brock's Marshtomp and everybody else's Pokemon, but they were saved by their trainers.
Marshtomp is a very loyal Pokemon. Even though he doesn't trust other people at first, he is still very friendly and a little bit shy. Like his trainer, he loves girls.