From Bulbapedia, the community-driven Pokémon encyclopedia.
Joshua (Japanese: ジョシュウ Joshū) is a minor recurring character who appeared in the Pokémon anime. He is Professor Birch's assistant.
He debuted in Get the Show on the Road. He was watching the lab while the Professor and Ash went to go look for Pikachu. When May arrived to receive her first Pokémon, Joshua informed her that the Professor was busy. May then went off to look for him.
In A Six Pack Attack, Joshua was taking care of the Hoenn starters for Birch.
Joshua made a short cameo in The Mastermind of Mirage Pokémon after Dr. Yung stole his and Birch's data to help construct his Mirage Pokémon.