Bowser, King of the Koopa

"The sorcerer king holding Princess Toadstool captive in the last castle. He comes at you spitting fire. There are several ways to kill him, but you only get points if you use fireballs." - Super Mario Bros. instruction booklet

This is Bowser (aka Koopa, aka Kuppa, aka King Koopa, aka Koopa King, aka King Bowser Koopa, aka King of the Koopas, aka Kerog), the main villain of the Super Mario Bros. video game series. The skin is based on his original sprites from Super Mario Bros. for the Nintendo Entertainment System, with the colors taken directly from the sprites.

And yes, the "King of the Koopa" title is intentional. It was taken from the instruction booklet, like the description above.