An incorrigible schemer, and the driving force behind almost all schemes that plague Macdonald Hall.
- Brainy Brunette: Dark haired and a Brilliant schemer.
- Berserk Button: Don't insult or try to change Macdonald hall. Also don't make fun of his lucky penny.
- The Chessmaster: Shows shades of this. He doesn't plan things as thoroughly as most examples but he's always got a plan and a contingency or two up his sleeve.
- Heterosexual Life-Partners: With Boots.
- Large Ham: Prone to giving Rousing Speeches
- The Leader
- Not a Morning Person: He always gets up at 8:45 and rushes to get to his first class at 9:00.
Melvin "Boots" O'Neal
Bruno's best friend, who consistently tries and fails to keep him out of trouble.
- The Ace: Captain of the hockey team and swim team, co-captain and backup quarterback of the football team, and capable of getting straight A's when he puts his mind to it.
- Butt-Monkey: Always seems to suffer the most from Bruno's scams.
- Embarrassing First Name: To him, anyway.
- Heterosexual Life-Partners: With Bruno.
- Known Only by Their Nickname: Not as much as he might like.
- The Lancer: To Bruno.
- Only Sane Man: In spades.
Mr. William Sturgeon (aka The Fish)
Macdonald Hall's Headmaster.
- Deadpan Snarker: He definitely has his moments—particularly when dealing with Miss Scrimmage.
- Early Installment Weirdness: In the first book he's much less sympathetic. When he sees Boots being chased by an angry George with a cricket bat he mutter that he hopes George catches him, whereas later books have him much more fond of his students, including absolutely refusing to expel Bruno despite Wizzle being adamant to do so. This is less due to Characterization Marches On, and more due to him being completely fed up with Bruno's undue influence on Boots: the book specifically has him trying to get both to reach their actual potential, and failing, and getting frustrated by it.
- Reasonable Authority Figure: Despite the image he has cultivated, he's actually very fair.
Macdonald Hall's resident genius.
- Berserk Button: People messing with his science experiments.
- Cannot Talk to Women: His throat closes up around girls.
- Early Installment Weirdness: In the first book he's more antagonistic to Bruno when the room together and is seemingly a loner with no interest in friends. From the second book onwards he's a close friend of Bruno and Boots as well as part of their larger social group, and very timid and soft spoken unless he hits his breaking point.
- Lovable Nerd
- The Smart Guy
- Teen Genius
Macdonald Hall's largest student and biggest eater.
- Big Eater: He's pretty much got a mini restaurant in his dorm room just for himself and bases most of his opinions/reactions on how they impact eating.
- The Big Guy: The schools largest student, capable of lifting a piano on his own despite being of middle school age.
- Berserk Button: Don't mess with his food. Also don't shorten his name to "Hacken".
- Race Lift: In The Movie series he's played by a black actor.
- Stout Strength: Based on his eating habits he's presumably more chunky than muscular, but he's the schools champion weight lifter and strong enough to lift a piano.
A very clumsy student.
- The Klutz: His entire character revolves around this. According to Bruno he could trip over a moon beam.
A not-too-bright student who's also part of the boys social group.
- The Ditz: Best exemplified when he couldn't wrap his head around the fact that you can't study for or fail an opinion test.Wizzle: Anderson, are you being deliberately dense?Pete: Sir?Wizzle: Never mind.
- When asked for his opinion on the poet Keats he stopped to ask the teacher what a "keat" is.
The office messenger and friend of Bruno and Boots.
- Flat Character: He's the office messenger and once roomed with Sidney. That's pretty much the extent of his characterization. Even in the The Wizzle War he's the only boy who didn't have a vendetta against Wizzle, he just liked being on committees.
- The Mole: As the office messenger he usually gets information about changes in the school in advance and fills the other boys in.
The school artist.
- Chuck Cunningham Syndrome: He's featured prominently in books 2-4 then seemingly disappears.
Walter C. Wizzle
The new assistant headmaster of Macdonald Hall. A computer nerd who's obsessed with the unnecessary modernization of the school.
- Arch-Nemesis: To Bruno.
- Happily Married: To Miss Peabody at the end of the book.
- Foil: To Mr. Sturgeon. Both are dedicated educators but while the fish is older, wiser and more reasonable but ultimately a bit too old fashioned and out of touch, Wizzle is young and naive albeit brilliant in some areas.
- Nerd: His glasses, style of dress and obsession with computers.
- Put on a Bus: To Hong Kong for a honeymoon. It was as far as the students could afford to send them.
- Technology Marches On: His idea for modernizing a school using computers came off a bit silly when the book was written, but nowadays computers are a staple of any school and the silly thing would be how primitive his system is for use in a school, especially a prestigious private school like the Hall.
- Well-Intentioned Extremist: He really did believe he was making the school better, he's just too naive to see that his ideas aren't as invaluable as he thinks.
Hank "The Tank" Carson
A former Macdonald hall student who went on to play pro football before retiring and opening a zucchini restaurant.
- Big Brother Mentor: To the team despite being more than old enough to be their father.
- Lightning Bruiser: Strong enough to carry a woman and two kids without strain, fast enough to take down Miss Scrimmage from a distance before she can pull the trigger on her shot gun.
- Nice Guy: Hands down the nicest adult in the series except maybe Mrs. Sturgeon.
- Stay in the Kitchen: Downplayed. Was quoted in a magazine saying girls can't play football during his playing days but seems to have abandoned that philosophy later in life.Carson: "Whoever said girls cant play football?Klapper: Psst. You did, Sports Illustrated interview, 1979.Carson: "Well, what do I know?
Miss Scrimmage's Finishing School For Young Ladies
Catherine "Cathy" Burton
Bruno's Distaff Counterpart and an accomplished schemer in her own right.
- Action Girl
- Brainy Brunette: Dark haired and rivals Bruno as a brilliant schemer.
- The Lad-ette: She grew up with multiple brothers, so this is understandable.
- Large Ham
- Sweet Polly Oliver: In The Zucchini Warriors.
Boots's Distaff Counterpart and Cathy's best friend. Her efforts to keep Cathy out of trouble rarely bear fruit.
- Flat Character: Doesn't get much characterization outside of being Cathy's roommate and Boots'so Distaff Counterpart.
- Hair of Gold, Heart of Gold: Described as blonde and much more kind-hearted than her roommate.
- Only Sane Woman: Usually the one trying to keep Cathy grounded.
Miss Eugenia Scrimmage
The headmistress and bane of Mr. Sturgeons existence.
- Cool Old Lady: Sometimes. She's very prim and proper but she's badass enough to take on all threats with her shotgun and the girls are actually very fond of her.
- Mama Bear: Endanger her students at your own risk.
- Sitcom Archnemesis: With the Fish.
- Women Are Wiser: Averted. She's generally the one to overreact and cause trouble compared to the more reasonable Mr. Sturgeon.
Miss Gloria Peabody
The new assistant headmistress in The Wizzle War who also happens to be an ex marine.
- Drill Sergeant Nasty: And how. She's got the girls doing morning calisthenics, marching and doing war games. Pretty unorthodox for a girls finishing school.
- For younger tropers unfamiliar with the concept of a finishing school(which is considered pretty outdated today) a finishing school is where girls learn to be well mannered and traditionally "lady like".
- Happily Married: To Wizzle in the end of the book.
- The Marine Corp: She's an ex marine through and through. Why she moved to Canada, which has no marine corp, is never brought up.
- Pet the Dog: She genuinely compliments Cathy on her hard work in the marching contest and war games, and describes her to Wizzle as "the best kid in school" die to her spirit and character.