Bowser was always named Koopa in Japan. He was renamed Bowser for some reason for the American releases (Probably to prevent confusion between Koopa Troopas and King Koopa).
The DiC cartoon referred to him as King Koopa, though they sometimes referred to him as Bowser.
Kelso: Guys this is a game of Cat & Mouse between me & Hyde. I''m gonna make him admit he''s been going out with Jackie behind my back.
Fez: Guys, what happens in Cat & Mouse if the cat is retarded?