Mr. Swampy (Japanese: ヌマタ老人Old Numata) is the Character of the Day in "A Mudkip Mission". He is the caretaker and breeder of many Mudkips living around a lake. His Mudkips later go on to be potential Starter Pokémon for new trainers. Upon first meeting Ash and friends, he thought they were there to steal the young Mudkips, but Ash explained that Brock was only saving a Mudkip with the help of an older Mudkip.
After Brock works together with the older Mudkip to stop Team Rocket's attempt to steal the young Mudkips, Mr. Swampy comments on how well they worked together and asked Brock to take Mudkip with him.
Mr. Swampy takes care of several Mudkips and Mudkip eggs on behalf of the Pokémon League. Team Rocket set their sights on the babies and destroyed a dam, flooding the area they lived in. Using his Forretress to keep the water back, Brock helped the babies to higher ground. Team Rocket soon appeared and captured all of the babies in a bag, but with the help of an older Mudkip, Brock's Lotad was able to save the Mudkips from capture.
Mudkip grew under Mr. Swampy's care but never left and stayed to watch over the new Mudkips born to marsh. After it helped save a baby Mudkip from being washed downstream, it worked together with Brock's Lotad to stop Team Rocket's plot to steal the younger Mudkips. Seeing how well they worked together, Mr. Swampy asked Brock to take Mudkip with him, to which he and Mudkip happily accepted.