Nat Faxon as Captain Underpants / Mr. Krupp (voice)

Jay Gragnani as Harold (voice)

Ramone Hamilton as George (voice)

Sean Astin as Narrator (voice)

Dayci Brookshire as Jessica / Dressy (voice)

Jim Cummings as Santa (voice)

Jorge Diaz as Melvin / Stanley Peet (voice)

Peter Hastings as Comic Narrator (voice)

Evan Kishiyama as Steve "Gooch" Yamaguchi (voice)

David Koechner as Mr. Meaner (voice)

Erica Luttrell as Erica / George's Mom (voice)

Patty Mattson as Miss Anthrope / Harold's Mom (voice)

Brennan Murray as Bo Hweemuth (voice)

Nolan North as Yule Tide / Lee Dingman / Movie Harold / Movie Santa (voice)

Kevin Michael Richardson as George's Dad / Movie George (voice)