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 searched for Pikachu, who ran away after suffering an electrical overcharge during an earlier encounter with Team Rocket. When May arrived to receive her first Pokémon, Joshua informed her that the Professor was busy. May then went off to look for Birch.
In A Six Pack Attack, Joshua was taking care of the Hoenn starters for Birch while he picked up Professor Oak from Littleroot Town's port. Oak, however, made his own way to the lab on his own after having to wait a while for Birch. May, Max, and Oak remained with Joshua momentarily, but they quickly left him in charge of the lab after Team Rocket stole all of the starter Pokémon. Joshua quickly alerted Birch to the situation via phone call.
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.
Joshua is a reliable laboratory assistant, often reminding Professor Birch of things and taking care of the lab while the Professor is out on his field expeditions. He remains calm even when under pressure.