Julius Oppenheimer Jr. is a delinquent trouble maker who goes to Elmore Junior High. Julius is a humanoid character with a black body and a bomb for a head styled to resemble classic cartoon characters from the 1920s and 1930s, wearing white gloves and a similar pair of shorts, along with a bow-tie. He is also monochrome to match the style. Julius is shown to take charge a lot. He seems to be bullying other students at Elmore Junior High. He is also shown to be quite smart. Even though he is considered a bully by the majority of kids at his school, he can get flustered quite easily.

He is a white rat wearing a grey hoodie. He also has red pupils. On his face is a red scar of unknown origin. He is shown to be very aggressive and violent, and shows signs of mental instability (i.e. his eye twitching). However, he is also very weak. He is part of Julius’s gang, taking part in pranks and bullying students.

He is a living severed hand that is capable of talking through a skull tattoo. He also has other tattoos, such as the word "HATE" inscribed on his fingers, and a cobweb tattoo just below his wrist. He is apart of Julius’s gang.

The rotten cupcake is an anthropomorphic rotten cupcake. He has muted pink icing, several sprinkles, and a rotten cherry on his head, the latter of which has been destroyed by Mowdown at least once. He wears a tan cupcake liner that has at least one pocket as his main form of clothing, which stretches over his arms and legs, over which he also wears black fingerless gloves and black boots. The rotten cupcake has been shown to be less violent than the other students who are regularly in detention. He is part of Julius’s gang.

Phillip, known by his nickname Mowdown, has pink fur and wears a white T-shirt with a red heart on it. Initially, the grizzly animal looks deceptively friendly (and even cuddly). Later on, he reveals claws, sharp teeth, and his true personality. He is also very large and strong. Mowdown pretends to be friendly, but then not too long after, he drops his disguise, and intimidates others by showing his teeth and claws. Judging by him being in detention often, he is very unruly. He is also violent. He is part of Julius’s gang.

Gumball is a twelve-year-old, blue male anthropomorphic cat that goes to Elmore Junior High, with his adopted brother Darwin and his four-year-old sister Anais. Gumball is a very imaginative person. Despite his mediocre academic performance, he can be surprisingly brilliant when it comes to formulating all sorts of mischievous schemes.

Darwin is an orange goldfish with arms and legs. His goldfish-shaped head takes up his entire body, with his fins and legs hanging down from it. He has retained his goldfish tail and fins, the latter of which he now uses as arms and hands. His legs are much longer than his body, ending with plain feet matching the color and texture of the rest of his body. Usually, though, he covers them with green and white sneakers. Darwin is a very happy and positive person. He is optimistic, always trying to see the best in most of the scenarios he is in, and in general, always tries to have a smile on his face. Not only does he desire to be happy, but he also desires to see others happy. He is 10 years old.

Anais Watterson is the youngest member of the Watterson family, the most intelligent, and can speak with an extensive vocabulary despite being only four years old. Anais is a small pink rabbit with a white-colored tail. She resembles Richard, her father, but is much smaller and shorter in physique and stature, has a more feminine appearance, does not have whiskers, and her ears curve in opposite directions as opposed to standing straight back.

Nicole is the mother of the Watterson family and is the backbone and only truly responsible member of the family. She is very dedicated to her family and would do anything in her power to keep them comfortable and safe. Nicole greatly resembles her oldest son Gumball, who is, like her, a cat. She has light cerulean fur and is somewhere between Gumball and Richard in height. Her head is shaped similarly to Gumball's, except with shorter whiskers, her nose is pink, and she has visible eyelashes. Her usual outfit consists of a short-sleeve collared white shirt with an orange, yellow, and green striped button that symbolizes her workplace, the Rainbow Factory, and a short, light gray pleated pencil skirt.

Richard serves the role of the father in the Watterson family. Unlike the traditional father, however, Richard is not wise, nor is he a good role model for his children in any way. Despite his misguided advice and uncouth mannerisms, Richard has good intentions and loves his family all the same. Richard has a similar appearance to his daughter, Anais. They are both pink rabbits, but whilst Anais is very small and slim, Richard is large and overweight. He has long, straight ears, a darker pink nose, three short black whiskers on both sides of his face. Even though he is unemployed, Richard is almost always seen wearing a work uniform, which consists of a long-sleeved, buttoned-up white dress shirt tucked into light brown pants, and a dark grey clip-on tie.