Nat Faxon

Captain Underpants / Mr. Krupp / Buffalobe (voice)

Jay Gragnani

Harold Hutchins (voice)

Ramone Hamilton

George Beard / Young Mr. Cleveland (voice)

Sean Astin

Narrator / Putter Mulligan (voice)

Dayci Brookshire

Jessica / Dressy / Smartaconda (voice)

Jorge Diaz

Melvin / Stanley Peet (voice)

Peter Hastings

Comic Narrator / Marlin (voice)

Evan Kishiyama

Steve "Gooch" Yamaguchi (voice)

David Koechner

Mr. Meaner (voice)

Phil LaMarr

Mr. Cleveland / Viper Chai (voice)

Erica Luttrell

Erica (voice)

Patty Mattson

Miss Anthrope (voice)

Brennan Murray

Bo Hweemuth (voice)

Nolan North

Lee Dingman / Hugo Mouthingwad (voice)