From Bulbapedia, the community-driven Pokémon encyclopedia.
The Diving Treasure Hunter (Japanese: トレジャーハンター Treasure Hunter) is a non-player character in Pokémon Ruby, Sapphire, and Emerald who exchanges Shards for evolutionary stones. He lives in a small hut on Route 124, near Mossdeep City. When the player talks to him, he will trade a corresponding stone for the player's Shard based on its color. This transaction is one of the few ways to obtain evolutionary stones in the Hoenn-based Generation III games.