Ash, Misty, and Brock met Bill at his lighthouse in 'Mystery at the Lighthouse'.
Bill had previously been trapped in a Kabuto costume for what he claims to have been hours (in the dub only; the original didn't state how long he had been in the costume) until Ash finally comes to press the release button for him. Afterwards, Bill fulfills a request made by Professor Oak to give Ash and his friends a lesson on the basics of Pokemon, during which Bill shares the idea that there may be many more than just 150 species of Pokemon. The remainder of his appearance is spent focused on explaining to Ash and company his recent project, involving a mysterious Pokemon whose cry can be heard across the sea.
Vova
