From Bulbapedia, the community-driven Pokémon encyclopedia.
Hal (Japanese: ヘイハチロー Heihachirō) is a character of the day who appeared in Beg, Burrow and Steal.
Hal is a scientist who lives and works on Izabe Island. He was looking for a hidden Pokémon paradise that he found when he was younger. He claimed that in the hidden paradise, he witnessed hundreds of Trapinch evolve into Vibrava. His childhood friend Elisa disagreed with him, and said the paradise could not possibly exist.
To prove his point, he attached a tracking device to a Trapinch and followed it around. Somehow, he, Elisa, along with Ash and his friends ended up underground. After finding their way through a series of tunnels, they stumbled across the very same paradise that Hal was talking about.
Not long after they stumbled across the paradise, everybody witnessed what Hal had witnessed many years before: hundreds of Trapinch evolving into Vibrava. Team Rocket appeared and tried to steal the newly-evolved Pokémon, but Brock, using his Ludicolo, along with Pikachu, freed the Pokémon and sent Team Rocket blasting off.
Elisa apologized to Hal for doubting him, and the Vibrava flew everybody out of the paradise.