Old Man Swamp is a man who runs a shelter for Mudkip and resembles the Pokémon he takes care of. He receives Mudkip eggs from the Pokémon League and raises them to be starter Pokémon for beginning trainers. When he saw that Ash and company trespassed in his secret shelter grounds, he thought that they were trying to steal the Mudkip. Soon everything was straightened out when Ash explained how Brock saved a baby Mudkip. But Brock explained to him later that another, older, Mudkip helped rescue the baby Mudkip.

Old Man Swamp has a tendency of giving out too much information. One instance was him telling Team Rocket not to break the dam because it would flood the area and the Mudkip would have nowhere to live.

When Old Man Swamp saw how Brock and Mudkip worked together to save the baby Mudkip and stop Team Rocket, he eventually asked him to take Mudkip with him as it was getting too old to give to a beginning trainer. Both Brock and Mudkip happily agreed.