From Bulbapedia, the community-driven Pokémon encyclopedia.
Sigourney (Japanese: シゲモリ Shigemori) is the character of the day from Claydol Big and Tall. He refers to himself as "the Sage of Izabe Island."
Sigourney lives a short distance from Mossdeep City. In the mountain range where he lives, he sells souvenirs to travelers in the area. He also tells stories of various Pokémon legends. The one he told Ash and his friends was about a giant Claydol that wrought havoc over the small town nearby. To stop it, an ancient wizard called the "White Sage" used a giant stone Poké Ball to capture it. The Ball fell into a lake, where it appeared to be safe.
Team Rocket decided to try to get the giant stone Poké Ball, but unwittingly freed the Claydol. It began to head towards the small village that it had tried to destroy hundreds of years earlier. Sigourney, with the help of Ash and the others, was able to capture the Claydol with another giant stone Poké Ball. Once again, it fell into the same lake the earlier one fell into. This time, Ash, Sigourney, and the others hoped it would stay there.