1. Nintendo characters; A race of turtle-like reptiles that come in all shapes and sizes. Most of them are Bowser's servants, but there are also a lot of good Koopas. Bowser's Koopas have many various soldier ranks, most common of which is "Koopa Troopas" (which is another word for "troopers", if I'm not mistaken).
2. Koopa is also the name of their king. Koopa or King Koopa, also known as Bowser or Lord Bowser. But anyone who watched old Mario cartoons or played Super Smash Bros. Melee on Japanese mode knows that already.
Ahem. Anyway, his full name (as far as I know) is King Bowser Koopa.
1. "Uh oh. There's an army of Koopas approaching us."
2. "Hi, Master Koopa! Whatcha doin'?"