Pirate Trainer

While Ash and his friends were waiting to eat, he approached them and asked Ash for a battle. Although he claimed he was too weak to work, Ash immediately jumped up, ready for battle (though in the Japanese version, he stated that he was just going to have a quick battle before lunch).

However, despite trainer's eagerness, Ash successfully knocked out all five of his Pokémon in rapid succession. In fact, Pikachu took out three of the Trainer's Pokémon in one Thunder Shock. The trainer was stunned by the defeat, and has not been seen since his brief appearance.

Notably, he had a then-unknown Generation II Pokémon when he appeared: a Donphan.

(Source: Bulbapedia)