From Bulbapedia, the community-driven Pokémon encyclopedia.
Dude is a Trainer on Route 29 right outside New Bark Town in Pokémon Gold, Silver, and Crystal. He notices the player pass by a few times and decides to teach him/her how to catch Pokémon. He is the Generation II equivalent of the old man, and was replaced with Lyra or Ethan in HeartGold and SoulSilver.
Caught in tutorial
The battle screen also shows that he has a single, unseen, Pokémon on his team during the capture tutorial.
- He, the old man, and Primo are the only NPCs to receive a back sprite, but not a front one.