To add a little elucidation to to the naming process of the six out of seven Koopa Kids:

Morton Koopa Jr. comes from Morton Downey Jr.
Wendy O. Koopa is based on Wendy O. Williams of The Plasmatics fame.
Iggy Koopa finds his name's origin in punk rock legend Iggy Pop.
Roy Koopa is based on our blind friend Roy Orbison.
Lemmy Koopa is based on Lemmy from Motorhead.
And Ludwig von Koopa is based on Ludwig von Beethoven, duh.

Well, I'm sorry I don't know how Larry Koopa got his name, maybe someone can help?