Main • Penn Zero (voiced by
Thomas Middleditch) is the main protagonist, a part-time hero and the son of two full-time heroes. Penn lives with his aunt Rose and uncle Chuck due to Rippen trapping his parents in a dangerous dimension known as the "Most Dangerous World Imaginable", and goes on part-time hero missions with his friends Sashi and Boone. While Penn is the recognized leader of the group, he is often advised by his friends and parents, contacting the latter using a MUHU (Multi-Universe Hologram Uplink). • Boone Wiseman (voiced by
Adam DeVine) is Penn's friend and a part-time wise man. Boone often bewilders his friends with his unconventional methods and thought processes, and at times they find him frustrating. However, Boone's unorthodox style has proven effective in helping his friends complete missions. His parents, like Penn's, were part-time heroes. • Sashi Kobayashi (voiced by
Tania Gunadi) is Penn's friend and a part-time sidekick. Sashi is often a voice of reason and understanding despite her demeanor, and informs the group of their missions using her futuristic glasses. Additionally, her parents are civilians and are initially unaware of her job until the second-season episode "The Kobayashis". • Phyllis (voiced by Sam Levine) is a grouchy, often irritable Slavic woman who maintains the Multi Universe Transprojector (MUT) used by Penn and his team to travel to other worlds and fight evil. The MUT is located in an abandoned theater called
The Odyssey, which is located next to the part-time villains' base at Fish Stick on a Stick. The episode "Zap One" reveals that she chose Penn and his parents to be part-time heroes, and the series finale reveals her to be the good half of the Guardian entity.
Villains • Rippen (voiced by
Alfred Molina) is the main antagonist, a part-time villain and an art teacher at Penn's high school. He aspires to become a full-time villain, which requires him to successfully accomplish an evil scheme without being thwarted by Penn's team. The second-season episode "Mr. Rippen" reveals that he is from another dimension and was chosen by Phil to be a part-time villain. • Larry (voiced by
Larry Wilmore) is Rippen's part-time minion and the principal of Penn's high school. However, he is not particularly villainous, and simply loyal to Rippen. Larry's futuristic glasses can project holographic displays with info on their missions, similar to Sashi. • Phil (voiced by Sam Levine) is Rippen and Larry's
Slavic assistant who operates their portal in the Fish Stick on a Stick restaurant. The series finale reveals him to be the evil half of the Guardian entity.
The heroes' family • Vonnie Zero (voiced by
Lea Thompson) is Penn's mother, a part-time sidekick who, because of Rippen, is trapped in the "Most Dangerous World Imaginable", with her husband Brock. She loves her son dearly, and understands that he misses them. However, she is capable of handling herself in a fight despite being an ordinary human. • Brock Zero (voiced by
Gary Cole) is Penn's father, a part-time hero who, because of Rippen, is trapped in the "Most Dangerous World Imaginable" with his wife Vonnie. Brock is part fearless fighter, part loving father, with a tendency to bring up embarrassing things during holographic chats with his son and Penn's friends. He also appears to have a rather antagonistic relationship with Penn's uncle Chuck. • Aunt Rose (voiced by
Rosie Perez) is Penn's aunt, who he is staying with while his parents are away. Rose appears to have little in common with her relatives, and Penn struggles with living with her and her husband Chuck. • Uncle Chuck (voiced by
Lenny Venito) is Penn's uncle, a balding man who is apparently uninvolved in the family hero business. The pair of them find other pursuits, such as dressing their pet chinchilla, more entertaining. • Sylvester (voiced by
George Takei) and Tia Kobayashi (voiced by
Lauren Tom) are Sashi's parents, who, unlike Boone and Penn's parents, were never part-time heroes. They discover that Sashi is a part-time sidekick in the second-season episode "The Kobayashis".
Recurring • Old Man Middleburg (voiced by
Jess Harnell) is an elderly resident of Middleburg and an old friend of Larry. • Alex (voiced by
Brandon Scott) is a friendly jock at Middleburg Central High. • Teddy (voiced by
Thomas Middleditch) is a student at Middleburg Central High School.
Residing in other dimensions • Scaley Briggs (voiced by
Beau Bridges) and Amber Briggs (voiced by
Olivia Holt) are a father and daughter from the town of Big Butte in a Wild West-themed world inhabited by cowboys and dinosaurs. Scaley is the sheriff of Big Butte before retiring in the series finale and passing the job to Amber. • Captain Super Captain (voiced by
Adam West) is a hero and electrician from a world inhabited by superheroes and villains. He possesses superpowers like flight, super strength, and energy manipulation. • Professor Evil Professor (voiced by Adam West) is the evil brother and the nemesis of Captain Super Captain who has a Ph.D in villainy. • Blaze (voiced by
Sean Astin) is a Flight School cadet from a world inhabited by humanoid
dragons. • Princess Argelbleccht Blunkenthorthph (voiced by
Elizabeth Henstridge) is the spoiled, beautiful princess of the Alien World. • Nug (voiced by
Maria Bamford) is a cavewoman from the Caveman Spy World and a member of the secret agency C.L.I.A. (Caveman Low Intelligence Agency). • Lady Starblaster (voiced by
Sigourney Weaver) is a space villain from the Galaxy World and Rippen's love interest. • Shirley B. Awesome (voiced by
Wanda Sykes) is a military action figure. • Maria (voiced by
Sonequa Martin-Green) is a pirate from the Pirate World. She is accompanied by Maria (voiced by
Yvette Nicole Brown), a living dolphin-like ship. • Milkman (voiced by
Paul Reubens) is a villainous milkman from Cereal World who ruins cereal crops with his milk. ==Production==