Old Man Swamp runs a shelter on Dewford Island for Mudkip and resembles the Pokémon he takes care of.
In A Mudkip Mission, he was initially furious to see that Ash and his friends had trespassed onto his property. Soon everything was straightened out when Max explained that Brock saved a baby Mudkip. But Brock explained to him later that another, older, Mudkip helped rescue the baby Mudkip. Afterwards, Swampy invited the group over to his home and allowed them to watch a Mudkip hatch from an Egg.
Team Rocket, who had accidentally stumbled onto Swampy's property were unaware of the valuable Mudkip the he was caring for. However this all changed when Old Man Swamp, who has a tendency of giving out too much information, revealed that he raised Mudkip and he explained that breaking the dam would flood the area and the Mudkip would have nowhere to live. James promptly called on Cacnea to destroy the dam wall, and soon the Mudkip were threatened by the raging flood waters. Brock, Lotad and the large Mudkip went onto rescue all of the Mudkip hatchlings. Afterwards, Team rocket revealed their mechanized Mudkip maiden and scooped up all of the Mudkip. Brock again intervened, having Lotad and the large Mudkip soak the ground to trap the robot in the muddy soil before Pikachu sent the Rocket trio blasting off with a Thunderbolt.
When Old Man Swamp saw how Brock and Mudkip worked together to save the baby Mudkip and stop Team Rocket, he eventually asked Brock to take Mudkip with him as it was going to be too lonely once all of the other Mudkip were given to their new Trainers. Both Brock and Mudkip happily agreed.
In A Mudkip Mission, one of the baby Mudkip fell into the river during a play fight, though Brock used his Lotad to save it and a bigger Mudkip helped them back to shore.
Later, Team Rocket appeared on Swampy's property and set about trying to catch the young Mudkip. Their initial attempt failed after Brock Forretress, Lotad and Mudkip rescued all of the hatchlings from the flood waters. Afterwards Team Rocket used their Mudkip maiden robot to scoop up all the Mudkip. However their plot was again thwarted, with Brock having Lotad and Mudkip use water Gun on the ground to trap the mecha in the mud. Mudkip went onto free all the young ones before Pikachu sent the Rocket trio blasting off with a Thunderbolt.
This wild Mudkip did not leave the swamp as it befriended many of Swampy's hatchlings and acted as a guardian for the younger, smaller Mudkip. It later joined Brock and left the pond after he helped it rescue itself and a younger Mudkip from a Team Rocket attack.