Koopa

A Koopa Troopa is an enemy in the Mario Series that first appeared in the game Super Mario Bros for the NES. They will either appear as red, green, blue (underground), yellow or purple, with green and red being the most common. The green ones will always fall off the ledge if there is one, while the red ones will stay on the platform there on. In most games, Koopa Troopas will sometimes grow wings and turn into Koopa Paratroopas.

After Super Mario Bros, they appeared in the game Super Mario Bros 3 for the NES. In the game, they did exactly what they did before, except there was a wide varity of Koopa Troopa species, such as a very large one, and Dry Bones.

Soon after Super Mario Bros 3, Super Mario World was released on the SNES. This was the first game to have the Koopa Troopas walk on two legs, instead of there usual four. The Four legs never appeared again in a game, untill the remakes of the classics, and in Mario and Luigi: Super Star Saga, but as a Troopea, a Beanbean Kingdom version of the Koopa Troopa.

Koopas might be related to the Shellcreepers in Mario Bros.

Father of Species
The Koopa Troopa is the progenitor of many other 'species' inspired by its basic concept, each including its own twist on the formula.