This gentleman is one of the guests of St. Anne. Though his Raticate was powerful, he saw how powerful Ash's Butterfree was in the battle and proposed a trade to Ash. While they made the trade, Ash wanted Butterfree back, so they traded the Pokémon back before the ship sank.
Raticate was a powerful Pokémon. When it battled Ash's Butterfree, the Gentleman stopped the fight. Later, he advised Ash to trade Butterfree for Raticate, which he did. However, Ash wanted Butterfree back, so he traded the Raticate back.