| Voice Actor | Lane Toran (as Arnold (Seasons 1–2)), Spencer Klein (as Arnold (Seasons 4–5)), Alex D. Linz (as Arnold (Season 5)), Jamil Walker Smith (as Gerald Johanssen), Francesca Marie Smith (as Helga Pataki), Dan Castellaneta (as Grandpa Phil), Tress MacNeille (as Grandma Gertrude "Pookie"/Miss Slovak), Justin Shenkarow (as Harold Berman), Christopher Walberg (as Stinky Peterson), Anndi McAfee (as Phoebe Heyerdahl), Sam Gifaldi (as Sid), Olivia Hack (as Rhonda Wellington Lloyd), Christopher Castile (as Eugene Horowitz (Season 1)), Jarrett Lennon (as Eugene Horowitz (Season 1)), Benjamin Diskin (as Eugene Horowitz (Seasons 2–4)), Blake McIver Ewing (as Eugene Horowitz (Season 5)), Ashley Buccille (as Lila Sawyer), Steve Viksten (as Oskar Kokoshka), Mary Scheer (as Suzie Kokoshka), Dom Irrera (as Ernie Potts), Baoan Coleman (as Mr. Hyunh), Maurice LaMarche (as Robert "Big Bob" Pataki), Kath Soucie (as Miriam Pataki), Adam Wylie (as Thaddeus "Curly" Gammelthorpe), Craig Bartlett (as Brainy), David Wohl (as Principal Wartz), Dan Butler (as Mr. Simmons) |
