Male Bloo's best friend and an elementary school student. He seems to come straight from school every day, as he is always wearing his backpack. He has a studious streak but is a total sugar addict who loves sweets like chocolate; if he eats too much, he turns into a maniac and runs all over the place. He usually plays the straight man, but he gets along well with Bloo and they are often on the same wavelength. While Bloo is usually the one coaxing Mac into things, they often end up causing trouble together when their interests align.

Male Full name: Blooregard Q. Kazoo. Mac's imaginary friend. A slime-like appearance with a 'mild-flavored devil' personality. He is selfish, does whatever he wants, and whines incessantly if anyone criticizes his actions.

Female Thanks to her driver's license, she has the most concrete profile info among the cast. She is a 22-year-old woman, 5'8" (172cm) tall, weighing 127 lbs (52kg), with red hair in a ponytail and green eyes. She currently works at Foster's Home for Imaginary Friends, taking care of the residents—essentially as a slave. She is responsible for almost all the housework at Foster's, as well as the protection and management of the imaginary friends living there. Since she takes care of everyone, she plays the role of a big sister to all the imaginary friends.

Female A 'something' that can only say 'Coco,' can only write 'Coco,' and is generally bizarre. She lays eggs that contain strange and unexpected items.

Male A massive, powerful bull-like imaginary friend. Despite his intimidating appearance, he is incredibly timid and soft-hearted. However, because of his immense strength and look, he can be terrifying when he actually gets angry. He loves potatoes and hates pepperoni. Since his creator was Mexican, he mixes Spanish into his speech.

Male He has scars on both sides of his face, and his left arm is stubby and barely usable. Stalk eyes protrude from his head, but the left stalk is bent and the eyeball is detached, rattling around. His left eye rarely blinks and often stays open even when he sleeps. The left eye was damaged by a basketball, yet strangely, his right eye remained fine after being hit by a lamp falling from the second or third floor in a Halloween episode. He is canonically the tallest among the imaginary friends. Standing 10 feet (304cm) tall and weighing 130 lbs (59kg), he has a muscular(?) build capable of lifting Eduardo for several seconds. He wears high-top basketball shoes that squeak like they're on a court no matter what surface he walks on. He takes great pride in helping other imaginary friends. He is bright, optimistic, and incredibly generous, but he is nice to a fault, apologizing even when he has done nothing wrong. He almost never says no, especially when asked for favors. In one episode, he fulfilled requests for everyone from Bloo and Mr. Herriman to bank robbers and escaping convicts. Bloo often manipulates him by faking sadness or illness. Additionally, Wilt has severe stage fright. He is exceptionally good at basketball—which is what he was created for—but he is generally athletic in all aspects. While he often seems like a pushover, he has self-respect and will stand up for himself when necessary, so he doesn't come across as a total doormat.