Paul is a rival of Ash in the Sinnoh region. He has a very closed personality and doesn't make friends very easily. He strives to find the strongest Pokémon he can possibly find and if they don't meet his expectations he releases them.
He faced Ash in a full battle and managed to defeat him by using some of his older Pokémon where as Ash only used Pokémon that he had caught in the Sinnoh region save only Pikachu. The two of them made a pact to have a rematch at the Sinnoh League.
The two faced off in the quarter-final round of the Sinnoh League. Ash took the early lead by defeating Paul's Aggron and Gastrodon. Paul fought back though defeating Buoysel, Staraptor and Torterra in a row. Infernape proved to be a powerful opponent and was able to defeat Paul. A bond between Ash and Paul was formed as they both began to respect each other after the battle.
After loosing to Ash in the Sinnoh League, Paul returned home and then challenged Brandon of the Battle Frontier.