A red Koopa Troopa from Super Mario Brothers |
A Koopa Troopa is a turtle in the Mario and Mario Kart video games. Most of them work for Bowser (i.e. they are the "bad guys"), but in Paper Mario some of them are on Mario's side, notably a blue-shelled Koopa Troopa named Kooper who helps Mario defeat Bowser.
There are many varieties of Koopas, but the original distinction was of color: green and red. In Super Mario Bros., green Koopas will go marching off into pits, while reds will have the sense to walk back after meeting an edge. There are also flying Koopas, called "ParaTroopas", which follow the same green = dumb, red = smart dictonomy, and Hammer Brothers, bipedal turtles who wear helmets and toss hammers. In Super Mario Bros., they were always found in pairs along ledges, but in later games this is not always the case.
Super Mario Brothers 3 introduced giant Koopas and ParaTroopas, Boomerang, Fire, and Sledge (hammer) Brothers, and "Dry Bones", a skeletal Koopa. In Super Mario World, eating different colored Koopa shells (green, red, yellow, and blue) will give Yoshi certain powers. Yoshi will merely spit out green shells, but red shells give him fire breath, yellow creates a sand cloud when he hits the ground, and blue allows him to fly.
"Koopa", as a character (as opposed to a class of enemies) is featured in Super Mario 64, as a turtle that you race for a star. He is a also a playable character in Super Mario Kart, a racing game. He has excellent traction, very good acceleration, but a low top speed. As a computer opponent, he has the ability to fire unlimited turtle shells at other players' karts. He is not featured in Mario Kart 64.
The word "koopa" is most likely a play on the word "kappa," which in Japanese lore is a turtle-like creature.