Simpsons - Names?

[Spax]

I was wondering if anyone knows the last names of these characters from 'The Simpsons' (if they actually have last names:) : Lenny, Karl, Otto, Willie (Groundskeeper)

[rja211077]

Apparently Otto is Otto Mann and t'others have never had their surnames mentioned. For anything and everything about the yellow-skinned ones, visit Springfield Nuclear Power Plant. www.snpp.com

[SavageMonkey]

Without actually going on SNPP I believe Lenny is "Lenny Leonardson" (sp), and Karl is "Karl Karlson". Not much help, but these are definitely referenced quite a lot in the episodes to remember this.

[shybearuk]

According to snpp.com Karl is actually Homer's former assistant, but Carl-with-a-C's surname is listed as Carlson. No mention is made of Lenny's surname