Characters: My Gym Partner's A Monkey
Voiced by: Nika FuttermanA human boy who was transferred from Chester Arthur Middle School to Charles Darwin Middle School by an accidental misspelling of his last name from "Lyon" to "Lion".
- Body Horror: At the end of Hyena and the Mighty, Adam gets beat up by random machines after threatening Rufus to stop crying and Adam's beating makes Rufus laugh and results in Adam getting injured and bruised. But he deserved it for the massive jerk he was being.
- Butt Monkey
- The Chew Toy
- Deadpan Snarker
- The Hero
- Jerkass Ball: The Hyena And The Mighty. Big time.
- Jumping Off the Slippery Slope: The Hyena And The Mighty. His abuse of Rufus Hyena. Particularly the scene where he threatens the hyena with physical violence to stop crying.
- The Napoleon
- Only Sane Man
- Stranger in a Strange School: A human boy accidentally sent to an animal school.
- Token Human
- Youthful Freckles
- Ambiguously Gay: Has some shades of this
- Clingy Jealous Guy
- Everything's Better with Monkeys
- Idiot Houdini: Whenever he does something that causes trouble, Adam is always the one who gets blamed.
- The Lancer
- Large Ham
Voiced by: Rob PaulsenA highly intelligent lowland gorilla who serves as the anti-bully at the school and often gives confusing wisdom to people. He speaks in a soft-spoken and nearly monotonous manner, often stringing together technical words as a matter of his normal speech.
- Ambiguously Gay: In The Hyena And The Mighty, he calls Rufus Hyena his sweet, implying the two may be in a relationship despite Rufus being a one shot character. However, later, he was seen being attracted to another female gorrila
- The Big Guy
- Deadpan Snarker
- Genius Bruiser
- Gentle Giant
- Break the Cutie: Quite a few episodes do this to her.
- The Chick
- Cute Clumsy Girl
- Dogged Nice Girl: To Adam.
- Shrinking Violet
- Stalker with a Crush: To Adam of all people.
Voiced by: Rob PaulsenAn easy-going, street-talking green tree python. He is an underachiever and excessive daydreamer who's gullibility allows him to believe anything he hears, which makes him a constant source of misinformation.
- Cloud Cuckoo Lander: His antics and personality make him border one being one
- The Heart
- Reptiles Are Abhorrent: Averted.
- Surfer Dude: Talks like this.
- The Stoner: Acts like one
Guadalupe "Lupe" Toucan
Virgil "Bull" Sharkowski
Voiced by: Phil La MarrA bull shark and the school's bully.
- Always Someone Better: His big sister is a way better bully than he'll ever be. He's extremely sensitive about this fact. Especially so when she managed to teach Adam to go frenzy in minutes though trolling. A concept he himself spent the whole episode trying to teach the ever oblivious Adam to no avail.
- The Bully
- Mobile Fishbowl: Wears a special headset over his gills to breathe while on dry land.
- Only Known by Their Nickname: He's mostly called "Bull"
- Annoying Laugh
- Break the Cutie: Insulted by Adam, cried several times throughout his episode, terrorized by Nurse Gazelle, threatened by Adam at one point
- Dark Is Not Evil: He's a spotted hyena but is easily one of the most sympathetic characters on the show besides Ingrid Giraffe.
- The Hyena
- Mood-Swinger: So very much.
- Ocular Gushers
- Puppy-Dog Eyes: He's downright ADORABLE when he pulls it off.
- American Accents: Southern
- Nerd Glasses
- Too Kinky to Torture: He seems to like everyone treating him like crap.
- Lady Looks Like a Dude: Although she more sounds than looks like, however, she does, for some particular reason, have a mustache
- Little Big Sister: She's older than Bull, yet he is bigger than she
- Pink Is Feminine: First seen wearing a pink outfit and her "head phone" are a hot pink
- Tomboyish Name: Euripides is a male name
- Your Mom: Her insults feature this
- The Scrappy: In-universe example.
Principal Poncherello Pegone Pixiefrog
- Dean Bitterman: Averted. Though on one occasion he threaten Adam to get Henry to stay in the schoolnote or else would send him to Siberia, though later he admit he was bluffing.
- Pint-Sized Powerhouse: He beats a rhinoceros in a wrestling match.
- The Napoleon
- Small Name, Big Ego
Mrs. Geraldine Sharon Warthog
Mr. Cyrus Hornbill
Mr. Maurice Mandrill
Voiced by: Dee Bradley Baker
Voiced by: Nika Futterman
Coach Tiffany Gills
Vice Coach Horace Ferret
Voiced by: Tom Kenny and Robert Goulet in Animal School Musical
Mrs. Eugenia Tusk
Nurse Jacquline Gazelle
- Dumb Blonde: She mentioned that she's got a brain the size of a peanut in "Inoculation Day".
- The Medic
- School Nurse
Ms. Gretchen Loon
Voiced by: Dannah Feinglass