Bowser

Bowser, formerly known as King Koopa in localisation, is the main antagonist of the Super Mario series and the ruler of the Koopas. He has been the archenemy to Mario ever since his inception in the original Super Mario Bros., and has continued to make appearances in every mainline Mario game.

In Super Mario 64, Bowser once again attempts to kidnap Princess Peach. This time, he invades her own castle and traps both her, the Toads and the Power Stars within the castle walls. He also tries to stop Mario from freeing Peach and the Toads 3 times before he is eventually defeated by his archenemy.

Bowser is fought as the boss of Bowser in the Dark World, Bowser in the Fire Sea, and Bowser in the Sky. In the first two encounters, he relinquishes a Key; In the last, defeating him completes the game.