The old man is the owner of the Wailord-shaped boat, which is known to take travelers to Hearthome City. When Ash and his friends decide to get supplies before leaving, the old man offers to watch their Pokémon on the ship, where Pikachu and the other Pokémon are left to their own devices and explorations. The old man falls asleep and fails to watch them. When the boat leaves accidentally, the old man uses his Mantine to help the Pokémon trapped on the boat before it goes over a waterfall.
This is a listing of the old man's known Pokémon in the anime:
Mantine first appeared when it was chosen by the old man to carry Ash and Dawn towards the ship that is heading towards a waterfall and save the Pokémon inside. Ash and Dawn ride on its back and swam very fast towards the boat. It was then asked to jump over the boat which it quickly did. As the boat was heading back to the dock, they were about to crash to a massive rock. Ash's Pokémon attacks it but a large chunk of rock flew towards them. Mantine was shown to be pretty strong as it was seen to be able to destroy the large chunk of rock into smaller pieces, saving the ship. This Mantine is larger than the size of average Mantine.