Other main characters in the series include the imaginary friends Wilt, Eduardo, and Coco, as well as Madame Foster's granddaughter, Frankie, who is responsible for maintaining order in the home.
In some episodes, other recurring characters appear, such as the imaginary friends Cheese and Jackie Khones, the girl Goo, and Mac's brother, Terrence.
Mac (voiced by Sean Marquette) is Bloo's creator (having imagined him at the age of three) and Terrence's younger brother, a short boy with brown hair.
Bloo (self-identified as Blooregard Q. Kazoo; voiced by Keith Ferguson) is a blue imaginary friend and the main character of the series.
He is an anthropomorphic blue domed cylinder and was created by Mac when he was three years old and was placed in Madame Foster's care home after an incident depicted in House of Bloo's.
[1][15] Bloo's selfishness is fully displayed in the episode Emancipation Complication, where he accidentally frees his friends but only does so to retrieve a battery for his Game Boy.
[16] Bloo is a failure who blames the world for his shortcomings; in episodes like Sweet Stench of Success and Beat with a Schtick, he alienates all the home's residents.
[20] Bloo is obsessed with attracting the world's attention and dreams of working in show business, which he briefly achieves with limited success.
Eduardo (voiced by Tom Kenny) is a big, hairy, purple, Spanish-speaking imaginary friend who resembles a mixture of a minotaur and one of the beasts from Maurice Sendak's storybook Where the Wild Things Are, with horns, a snout, a pointy demon-like tail, and large teeth.
Despite his large and imposing size, overwhelming strength, and menacing appearance, Eduardo is usually docile, timid, somewhat overly sensitive, crying at minor negative occurrences, and scared of almost everything, most of all spiders.
[1][2][27] However, he can be ferocious if angered or when danger befalls one or more of his friends, as demonstrated in the episode Eddie Monster, where he overcomes the scariest imaginary creations of teenagers.
He once had a puppy named Chuy ("Chewie"), who turned out to be an imaginary dog with the ability to speak and bite with ferocious playfulness.
[33] No one knows who her creator is as she was found on a South Pacific island by two scientists named Adam and Douglas, who brought her to Foster's Home for Imaginary Friends.
Frankie has red hair tied in a high ponytail and typically wears a white T-shirt, a green zip-up hoodie with a hood, a denim skirt, orange socks, and sneakers.
[37] Mr. H. Herriman (voiced by Tom Kane) is a gray and white, large, elderly, anthropomorphic, lop-eared and rabbit-like imaginary friend with an English accent imagined by Madame Foster.
It was revealed in "Busted" that Mr. Herriman is so hard on Bloo because he feels that, given that he is allowed to stay at Foster's even though he still has an owner, he has already broken one of the main house rules.
[8][19] He is extremely fond of his creator, Madame Foster, harboring great respect and loyalty to her, even at her most prominent levels of unabashed pep and energy.
In Madame Foster's youth, Herriman created a lullaby named Funny Bunny, which causes him great embarrassment today.
According to McCracken, the imaginary friends are created in a child's mind to protect them, provide companionship, and fill the void of loneliness.
She believes in the center's purpose so deeply that, despite the overwhelming tasks and ungrateful work, she continues to carry out her duties, and the residents treat her like an older sister.
[46] Another character, Jackie Khones, originates from an unrealized idea by George Lucas for a sidekick to Lando Calrissian in The Empire Strikes Back.
[48] The gallery of supporting characters was created by the series' creative team, including Mike Moon, Ed Baker, Shannon Tindle, David Dunnet, and Benjamin Balistreri, who won multiple Emmy Awards for their individual achievements on the show.
David Cornelius, a journalist from DVD Talk, described the range of imaginary friends as diverse: from clumsy whims of childlike imagination to highly intricate creatures varying in shape and size.
[50] Bloo was described by Cornelius as resembling a ghost from the video game Pac-Man;[50] a deeper analysis of the character was presented by Mike Pinsky from DVD Verdict.