Captain Kusunoki

Captain Stern is the curator of the Oceanic Museum. He was introduced to Ash and Max when Marius battled them and lost; Captain Stern stepped in and mentioned he had been looking for Marius. As the curator of the Oceanic Museum, which Ash and Max attempted to enter, he offered to give Ash and Max a tour. The museum had many sculptures of Water-type Pokémon and models of submarines.

Captain Stern used underwater exploration vessels to explore the ocean, gather rare artifacts, and study sea Pokémon in their natural habitats. Captain Stern then showed off his latest find, a volcanic rock formed by underwater volcanoes, supposedly created by the Legendary Pokémon, Groudon.

While the kids went to go get ice cream, members of Team Magma broke in and stole the stone.

Ash had confronted the member of Team Magma when Captain Stern caught up to them, and he sent out his Sealeo, which used an Aurora Beam. The blast caused the thief to drop the case and Marius caught it. Captain Stern told Max and Marius to run for it, and they escaped via the sea using Spheal. Ash, however, refused to run and continued to fight. After another flurry of attacks, the case opened and the stone broke. Team Magma got half of the stone; Pikachu got the other.

Later, Ash apologized to Captain Stern for letting Team Magma escape, but Stern was grateful to just keep half of the stone so he could study it.

(Source: Bulbapedia)