Nat Faxon

Captain Underpants / Mr. Krupp (voice)

Jay Gragnani

Harold (voice)

Ramone Hamilton

George (voice)

Sean Astin

Narrator / Mr Gigglenose (voice)

Clancy Brown

Mr. Ree (voice)

Jorge Diaz

Melvin / Stanley Peet / Melvin's Dad (voice)

Peter Hastings

Comic Narrator (voice)

David Koechner

Mr. Meaner (voice)

Erica Luttrell

Erica / George's Mom (voice)

Brennan Murray

Bo Hweemuth (voice)

Kevin Michael Richardson

Diddlysaurus / George's Dad (voice)

Mindy Sterling

Melvin's Mom (voice)

Stephen Tobolowsky

Creepy Rattlechains (voice)

Kari Wahlgren

Mayor Hoppy McChapper (voice)