Guppy

Guppy is a plump and large killer whale who you race on many missions in Super Mario Galaxy. Despite his name, his very cunning and cheats his way to the sea. Althought he appears harmless, and you don't have to harm him, the Toad Brigade greatly fears Guppy. Penguins, however, are deeply annoyed by him. Even though he mean, he gives you tips on swimming.

Super Mario Galaxy
Guppy is seen in the Sea Slide Galaxy, where you have to race him by going through loops in the sea.

Guppy once again appears in the Deep Dark Galaxy, and, for the same reasons, have to go throught 8 loops to beat him.