He is a man who is believed to be able to dodge lightning.
After Goku failed at Kami's task of retrieving the crown on Mount Goro-Goro, Mr. Popo sends him to a forest in search of someone who can train his mind and teach him the technique that will allow him to avoid the lightning strikes on Mount Goro-Goro.
In the forest, Goku meets Mousse and is taken to the woodsman's home. Upon hearing his story, Mousse and his family tells Goku about Yaochun, the strongest man around. The grandfather of the family, Korinto, leads Goku to Yaochun who was meditating near a river. Goku asks Yaochun for a fight. Besides his large body and strong appearance, Goku was disappointed when he discovered that Yaochun was actually quite weak. It would later appear the man Goku was supposed to meet in the first place was Korinto.