Roy Koopa

Roy is the 3rd oldest Koopaling.

He might not be the brains of the Koopas, but he knows everything there is to know about how to make you hurt. Roy is, actually, very loyal to his father and the magnanimous Koopa Troop... or at least as loyal as a power-grubbing evil Bowser-spawn can be. He's definitely the sort of Koopa you'd be best to keep on good terms with.

Games
Roy is the boss of Sky Land and the Forest of Illusion in Super Mario Bros. 3 and Super Mario World, respectively. In both games, his trademark attack is a ground-shaking stomp to the ground, which paralyzes Mario for a few seconds, leaving him open to an attack from the Koopaling.

Cartoons and Comics
In the cartoons, he was named Bully Koopa, and he acted according to what his name implied. Also, he spoke with a gruff Brooklyn accent, voiced by Gordon Masten. Names aside, Roy doesn't seem to have any significant differences from his cartoon counterpart.

The comic books, however, did not carry the accent trait over, because Roy spoke in a standard English dialect in his one major Nintendo Comics System appearance. Incidentally, in the comics, it was revealed that he had a pet bunny named Pookie, whom he would often beat for Bowser's amusement.

Super Mario Bros. 3
Roy Koopa is so heavy so that he caused smaller earthquakes when he jumped. These quakes stunned Mario and Luigi for some seconds leaving them defenseless.

Super Mario World
Roy attacks Mario in a small closed room. First he tries to charge over him and then walks up the walls and then continue up-side-down in the top of the room in the ceiling. When Roy is directly above Mario he releases his grip and tries to fall down on him.

Yoshi's Safari
He guards course 7, the Float Castle 1. Roy attacks Mario and Yoshi from high up in the air in an balloon equipped with no less than 6 cannons.

Trivia

 * Roy is named after late country singer Roy Orbison.