Simplify the following text for a Grade 6 native English-speaking person.
Original: He is the first Asian swimmer to win a gold medal in Men 's 400 metre freestyle event , and the first Korean to win a medal in swimming .
Simplified: He is the first South Korean swimmer to win a world title . He won a gold medal in the men 's 400 meters freestyle final at the World Swimming Championships in Melbourne , 2007 .