• English / United States: Marlon
• Japanese / Japan: シズイ
• Japanese (Romanized) / Japan: Shizui
• Japanese (TL) / Japan: Shizui

Marlon is the gym leader of the Seigaiha Gym in East Isshu. Trainers that defeat him receive the Wave Badge. He was first seen in the anime on top of his Wailord as it came close to the beachline where Ash Ketchum and Cameron were. Marlon speaks with a heavy accent in the Japanese version.

Gym Battle Against Cameron

Marlon told Cameron that he'd stop him with his deep love for the sea. Marlon instructed that the Gym battles at the Seigaiha Gym are two Pokémon apiece and whoever defeats both first wins. Initially Cameron thought he did well in the battle and was going to have an easy victory in the match by quickly defeating Marlon's Jellicent but Marlon's tactic was revealed when Marlon's Jellicent Ability Cursed Body disabled Cameron's Ferrothorn Thunderbolt.

Marlon's Mantine tried to turn the tie of the battle to Marlon favor but Cameron's Samurott was able to hold its own in the water and give the match victory to Cameron. Marlon was actually quite impress with Cameron as he was able to make the special field his own.