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In "For Sale by Loner", he claims his father was a strict coach for him about wrestling at highschool. The son's sport efforts was never good enough for the father, what caused the former to hate sports.
In "Schooled!", it is revealed in his early life that he spent 15 years in the military. During that time, he also spent two months stranded inside a volcano eating lizards and his only tool being a pumice stone. Also, he has switched levels from being a seventh grade teacher to a sixth grade teacher and switched classrooms.
Mr. Bolhofner is first seen in "Middle Men" when Lincoln and Clyde attend his class as part of their middle school orientation. When Lincoln and Clyde take Byron and Cici's seats where they state that there are assigned seats in this class, Mr. Bolhofner scolds Byron and Cici for not being in their seats and gives them zeros.
In "Schooled!", Mr. Bolhofner is now teaching his class in a wooden trailer that is poorly air-conditioned, where he has Lincoln and Chandler as two of his students. In addition, he has bad breath from the food he eats and owns a pet piranha named Hank. After Chandler kicked Lincoln's chair which interrupted his teaching, Mr. Bolhofner punished Lincoln by having him join him for lunch. When Lynn locked Lincoln in the locker and had to explain to him why he was late, Mr. Bolhofner didn't care about that and punished him by having him join him for another lunch which got extended to a week when he asked if he can talk to the principal. Due to Chandler tampering with Lincoln's desk, Mr. Bolhofner had him sit in a loaner from the elementary school and sit near Hank. He only allowed Lincoln to go to the nurse's office after Hank bit him, but asked Lincoln to give Hank his tooth back on his way out. He does as Lincoln used this plan to gain an audience with Principal Ramirez. Once Lincoln returns to Royal Woods Middle School from Mapleton, Ontario, he persuades Mr. Bolhofner to turn down the thermostat. Mr. Bolhofner starts to get angry at first. To his students' surprise, Mr. Bolhofner ends up doing so as nobody had asked him to do that before as he decreases the temperature from the low 90s to the low 80s. This caused most of the students to rejoice.
In "Kernel of Truth", Stella interviews Mr. Bolhofner about his birthday and suspected that he was in his 60s. Mr. Bolhofner angrily states that he is 34 and slams the door to his wooden trailer. Principal Ramirez later states to Lincoln and his friends during her feedback of their revived news program that Mr. Bolhofner is suing the school.
In "No Bus No Fuss", Rita accidentally pulls Vanzilla out in front of Mr. Bolhofner's car which angers him causing Lincoln to duck out of sight. While in the cafeteria, Mr. Bolhofner cuts in front of Lincoln in retaliation and says, "See how it feels, Loud? Tell your mother I said hi."
In "Flying Solo", Mr. Bolhofner becomes the head of the home-ec club which Stella, Rusty, and Zach join hoping to make cookies. After mentioning that he once survived in the Amazon Rainforest, Mr. Bolhofner states that they will be making cricket cheesecakes. Mr. Budden later contracted the home-ec club to make the outfits for the glee club. For Lincoln and Clyde, they got survivalist-type outfits that were the ideas of Zach and Mr. Bolhofner as both of them give each other the thumbs up.
"Rumor Has It" marks his first major role. In the episode, Mr. Bolhofner drives Lincoln and his friends, who are already terrified that he is coming on the trip overseen by Mrs. Salter and are believing rumors about Mr. Bolhofner's shady past, to a field trip on his van, though the trip is cancelled when he gets a text from Mrs. Salter that the school bus got stuck in Flippee Syrup. He tries to drive back to the school, though a tire on his van pops. He is forced to take the kids into his run-down and creepy cabin for the night. Throughout the night, the kids try to escape, eventually locking him in a cellar, though the moment they finally do, they are cornered by a dead end. Mr. Bolhofner, who has escaped from the cellar, fights with the bear that was coming near them, causing it to run off into the woods, scared. Mr. Bolhofner sees the true reasoning behind the kids' wanting to escape, and sees himself outside so they don't have to worry about "Skullhofner". The kids feel bad, though they make it up by presenting the video of him wrestling the bear, dubbing him "Coolhofner" to the students and Mrs. Salter. Touched, he thanks Lincoln and his friends for showing that he, despite having a rough exterior, is a cool and loyal man on the inside.
In "For Sale by Loner", Mr. Grouse moved next to Mr. Bolhofner and tried to befriend him as new neighbour, but he was too much stubborn to make it happened. After many antics of Mr. Grouse, Mr. Bolhofner got frustrated and told him to leave, because he disturbs his peace and quiet.
Having spent 15 years in the military, Mr. Bolhofner treats his students as soldier or recruits. He also got used to food found in wilderness like bugs.
He is a very strict teacher, who demands a lot from his students and punishes them for minor misdeeds like not being in their assigned seats during his classes. He also expects kids to be on time for class, lest they are hit with detention, as seen in "Rumor Has It". When he has an issue with an adult, he takes his revenge on the adult's child like in "No Bus No Fuss".
However, he has also a cool side, as he allows successful athletic students to pass without quizzes. He is willing to change things that do not bother him like turning down the temperature in his class when Lincoln asked politely. This cool side is also seen in "Rumor Has It" where he saves Lincoln and his friends from an angry bear; seeing Lincoln and his friends prove to everyone that he isn't what he seems to be based on false rumors, he is grateful and accepts the nickname "Coolhofner".
Despite his short temper and strictness, he's sensitive about students and teachers spreading bad rumors about him like being an escaped convict, a cannibal, or a gangster.
For unknown reasons he stopped caring about his hygiene, because since "Schooled!" he goes to work in unwashed clothes, doesn't shave his face, does nothing to his messy hair and doesn't brush teeth.
He is a tall, dark tan-skinned man. He has dark greasy hair, two thick black eyebrows, and a black mustache. He wears a light yellow polo shirt, with a green stripe across it, green trousers, with a black belt buckled in, and brown shoes.
In Season 5, he now has a sloppy appearance where is now sporting facial hair, his hair is much messier, his shirt is stained, and his pants now have a patch on it, in addition to his shoes tops being taller, resulting in them sticking out of his pants.