Nat Faxon
Captain Underpants / Mr. Krupp (voice) (7 eps)
Jay Gragnani
Harold (voice) (7 eps)
Ramone Hamilton
George (voice) (7 eps)
Sean Astin
Narrator (voice) (7 eps)
Peter Hastings
Comic Narrator (voice) (6 eps)
Jorge Diaz
Livmen / Stewart / Statrew (voice) (1 eps)
David Koechner
Mr. Meaner / Mr. Nearme (voice) (1 eps)
Erica Luttrell
Arice (voice) (1 eps)
Laraine Newman
Elbrib (voice) (1 eps)
Secunda Wood
Moxie Swaggerman / Xemio (voice) (1 eps)