List of Uncle Grandpa Characters.
- Uncle Grandpa (voiced by Peter Browngardt): The series main character, Uncle Grandpa has an L-shaped head, a pink nose, a red fanny pack that talks, a propeller hat, and overalls. He appears very stupid and has many floating heads and differently random bodies. He would make anything awesome for the kids. His catchphrase is "Good Morning".
- Belly Bag (voiced by Eric Bauza): Uncle Grandpa's talking red fanny pack who holds all of his priceless valuables. He even has an elevator inside of him that can lead to many secret dimensions.
- Pizza Steve: (voiced by Adam DeVine) A talking pizza with sunglasses who is friends with Uncle Grandpa. He believes he is the best thing in the world.
- Mr. Gus: (voiced by Kevin Michael Richardson) A large green lizard who is Uncle Grandpa's sworn protector and body guard. He is obviously a parody of Godzilla.
- Giant Realistic Flying Tiger: A photoshopped real photograph of a tiger that Uncle Grandpa rides on to get around.
- Beary Nice: (voiced by Audie Harrison) – A teddy bear accompanied by Hot Dog Person, and who sees the world as being very nice, but doesn't notice Hot Dog Person when he is in danger, and he usually ends up with good experiences. His catchphrase is "That's me!".
- Hot Dog Person: (voiced by Eric Bauza) – A hot dog accompanied by Beary Nice, and who sees the world and new things as being very dangerous, he usually ends up having bad experiences. His catchphrase is also "That's me", but in a sad, depressed voice.
- Tiny Miracle: (voiced by Tom Kenny) – Tiny Miracle is a robot that can perform miracles by just a series of unnecessary moves, and then technically performing the miracle only to lead up to another tiny miracle. He sounds like a 1980s microphone. According to Mr. Gus, he is Uncle Grandpa's helper. He can be summoned by saying "It'll take a tiny miracle to..." and then the task the person is attempting. His catchphrase is "Did somebody say "tiny miracle"?"
- Charlie Burgers: (voiced by Brian Posehn) – A talking dog that befriends Uncle Grandpa and his friends. He can be well behaved and he enjoys going on adventures with Uncle Grandpa. His catchphrase is "I love my ball!"
- Frankenstein: (voiced by Mark Hamill) – A tag-along with Uncle Grandpa in his adventures. Frankenstein appears randomly in the series, but rarely, if ever, has anything to do with the plot. Because of the condition, he is unable to talk, though he will occasionally roar. He is usually seated next to Uncle Grandpa in his chair.
- Xarna, She-Warrior of the Apocalypse: (voiced by Eric Bauza) − An overly-muscular, masculine female warrior. She is on a mission to get some gas for her motorcycle. Her catchphrase is "I don't like your mouth."
- Aunt Grandma/Priscilla Jones: (Voiced by Lena Headey) − Uncle Grandpa's nemesis with a British accent who wants revenge on him for ruining her science project and rather than help her played hacky sack instead resulting in her getting second place in the science fair. She prefers to solve children's problems using simple practical solutions, the complete opposite of what Uncle Grandpa does. Her catchphrase is "Beautiful Morning!"
- Evil Wizard: (Voiced by Rob Schrab) − A wizard that goes around trying to make everyone's day horrible by humiliating them but he actually makes their lives better. His catchphrase is "Behold! I am Evil Wizard!"
- Crazy Baby: - is the main antagonist of Driver's Test. He is voiced by Eric Bauza.
- Angry Man Johnson:(voiced by Roger Craig Smith) – Angry Man Johnson is a grumpy man who hates Charlie Burgers. Judging by his name, he is always angry at everyone, including Uncle Grandpa. Angry Man Johnson frist appears in "Charlie Burgers".
- Belly Boy:is a boy that appeared in the episode Belly Bros. In the beginning of the episode, he was not able to put his shirt on because his belly was too large. Uncle Grandpa made him a shirt but it accidentally transported him into the night wolf dimension. After him and Uncle Grandpa go on an adventure to defeat the Night Wolves and get home, Belly Kid comes to love his belly and decides he does not need a shirt. He is voiced by Zachary Gordon.
- Melvin:Melvin is a character who appeared in the series Uncle Grandpa in the episode "Space Emperor". He is voiced by Jarid Root.
- Eric:Ericis a kid who appeared in the episode "Nickname". During the episode he was being made fun of by kids for not having a nickname, so he tried to earn one by doing yard work. He eventually obtained the nickname Cupcake. He is voiced by Eric Bauza.
- Mary:Mary is a teenager that appeared in "Driver's Test". Before Uncle Grandpa helped her get her license, she kept on failing her driver's test. She is voiced by Pamela Adlon. She is also a minor character of Uncle Grandpa.
- Dennis:is a character that appears in "Uncle Grandpa Ate My Homework!". He is voiced by Tom Kenny. Dennis has a skeptical nature and often questioned Uncle Grandpa's antics. He's also quite easy to irritate and is quick to get impatient (as shown in Uncle Grandpa Ate My Homework when he yelled at Uncle Grandpa several times about eating his homework and picking the buttons in the elevator). However, this irritation and impatience may be a direct result of the situation Uncle Grandpa put him in. Dennis doesn't seem to be doing too well in school, considering the project he was doing would determine whether or not he would pass his class (also because Mrs. Numty figured his Uncle Grandpa Adventure was an excuse he made up and scolded him for perhaps putting more effort into his work than his excuses). This could be because Dennis procrastinates (working on a school project the night before it's due) or because Dennis does not follow the school's orderly structure (since he is skeptical and impatient by nature as we see throughout the episode).
- Guillermo:Guillermo is a character that only appeared in "Uncle Grandpa for a Day". His bike was accidentally crushed by The UG RV, and because Uncle Grandpa and Belly Bag had jars of peanut butter stuck on their heads, it was up to Mr. Gus and Pizza Steve to help out Guillermo. He is voiced by Eric Bauza.
- Susie:is the little girl in "Afraid of the Dark." During the episode she was afraid of the dark, but over the course of the episode Uncle Grandpa helped both, himself and Susie get over their fear of the dark. Unfortunately for her mother, in the process of getting rid of the fear, she ended up destroying her room. She is voiced by Grey Griffin.
- Adam: is a minor kid in Uncle Grandpa. He first appeared in "Belly Bros" when Belly Bag was telling Belly what Uncle Grandpa is. He officially first appeared in "Brain Game", he needed Uncle Grandpa and Pizza Steve's help beating a video game that he could not beat. He is voiced by Dee Bradly Baker.
- Austin (also known as Austin 2.0): is a kid and the main antagonist of the episode "Perfect Kid". He is also one of minor characters in the series Uncle Grandpa. He is voiced by Carlos Alazraqui.
- Akira:is a kid who appears in the episode Big in Japan. He is voiced by Jessika Van.
- Nurbert Nimbo:
- Little Jimmy:
- Chad:is a boy who appaers in the episode Custom Crisis.
- Kimmy: voiced by Tress MacNeille.
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