King Bowser Koopa (known in Japan as 大魔王クッパ Daimaō Kuppa "Great Demon King Koopa") is the main antagonist of the Mario series. His first appearance was in Super Mario Bros., and has been a recurring baddie/boss ever since.
Bowser looks very similar to a Koopa (due to him being one). Bowser is the king of all Koopas. Though he is a Koopa, he lacks the harmless look. Bowser has spikes growing from his back and emerges from an even bigger shell. Bowser has a distinguished look on his face making him look like a demon (hance his Japanese name). Bowser also has a nose ring, another reason why he looks so different from other koopas.