Nat Faxon
Captain Underpants / Mr. Krupp (voice)

Jay Gragnani
Harold (voice)

Ramone Hamilton
George (voice)

Sean Astin
Narrator / Mr Gigglenose (voice)

Dayci Brookshire
Jessica / Dressy (voice)

Clancy Brown
Mr. Ree (voice)

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

Peter Hastings
Comic Narrator (voice)

Evan Kishiyama
Steve "Gooch" Yamaguchi (voice)

David Koechner
Mr. Meaner (voice)

Erica Luttrell
Erica / George's Mom (voice)

Patty Mattson
Miss Anthrope / Harold'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)