Mr. Cheetah is a one-time villain from the classic Cartoon Network series, My Gym Partner's a Monkey, only appearing in "Lie, Cheetah, Steal". He is a bodybuilding athletic cheetah who started involuntarily working at Charles Darwin Middle School, where he stole Horace's and later Coach Gills' job, as a way of working his way up to stealing dethroning the school principal and taking the school over for himself. As a worker who was never hired to begin with, Cheetah is part of the Unapproved Teachers Union.
In "Lie, Cheetah, Steal", Coach Gills was abandoned by her assistant, Horace. This immobilized her and made her late for gym. Eventually, Mr. Cheetah entered and explained that Horace was absent, so he'd be taking his place. When Coach Gills fist laid eyes on him, she instantly fell madly in love. Cheetah explained that Horace was a friend of his and his absence was on account of him throwing his back out, and the reason for that was because he was his personal trainer and he overworked him. The two of them decided among themselves that he'd be filling in for him at school. Coach Gills didn't consider the unlawfulness of this and just went along with it, because she loved him and was excited to have him as an assistant.
In gym that day, Coach Gills went through her usual business, screaming at her students like a drill sergeant. She was yelling at them to climb a rope and they were all doing pitiful jobs. Mr. Cheetah assured Coach Gills that if she kept treating her students like that, none of them would make any progress. He then demonstrated to her, teaching Adam and Jake with a more positive approach. Mr. Cheetah showed off his amazing gymnast skills and amazed by his athleticism, the students wanted to be more like him, which got them interested in his nice and easy-going gym lessons. At the end of the day, everyone loved Cheetah, and Coach Gills loved him even more and in a bit different of a way.
Coach Gills worried that Mr. Cheetah would steal her job, which was a plausible fear, given how much better he was at doing it. Mr. Cheetah blatantly lied to her, saying that he'd do no such thing, despite his extreme physical advantages over her, including him being the fastest land animal in the world, not needing to drink water, and the ability to change directions in mid-air due to his extremely flexible spine. On top of that, students liked him more anyway and he was overall, a far more decent coach. This didn't mean he was going to steal her job, though.
Before Coach Gills knew it, her office had already been taken over by Mr. Cheetah. Not only this, but all of her students were now completely ripped. Adam and Jake overheard him having a phone conversation with his mother, where he explained his success with overthrowing Gills. He then said that he'd later move on to overthrowing Principal Pixiefrog as well. Adam convinced Jake that Principal Pixiefrog was their friend and they needed to stand up for him.
Principal Pixiefrog said that since Mr. Cheetah technically never even worked for him in the first place, just being a friend of Horace's, he was unable to "fire" him. Their only alternative was getting him to resign in shame. Coach Gills had to compete with him in a series of physical contests, so that they could attack his weak spot, his obsession over his body and athletic skills. A feat like this would be next to impossible, since Mr. Cheetah was a cheetah and Coach Gills was a mere goldfish, who didn't know how to swim.
Coach Gills and Mr. Cheetah faced off in the competitions, but everyone was cheering for Cheetah, with Adam and Jake being the only ones on Gills' side. Their first competition was to run a lap around the school. Mr. Cheetah started and finished in a second and Gills couldn't leave her bowl. The same thing happened for their swim race in the public pool. The last contest was a tree climbing race, which he won once again. Jake noticed that Mr. Cheetah used his claws, when climbing the tree, which was against the rules. Adam and Jake called him out on cheating. Mr. Cheetah shamelessly admitted to this and effortlessly threw in the tower, congratulating Jake for his good eye, Adam for his obedience to the rules, and Coach Gills on getting her job back. He then walked away, simply not caring that he was defeated.
Mr. Cheetah is athletic, narcisistic, and gets on the good sides of even his enemies. He applies good sportsmanship to battles with his enemies, which only angers the opponent. He is obsessed with power and dominance and it's become his goal to reach the top of whatever it is he does. He even attempted overthrowing Principal Pixiefrog as the head of Charles Darwin Middle School. His friendly appeal gets him on the good sides of people he targets as either enemies or victims. Nothing seems to stunt him, as he happily accepts defeat if he loses fair and square. For someone who honors fairness and good sportsmanship so much, he sure does cheat a lot, which he admits to full well, yet takes no action to try and put a stop to.
He's one of the few one-time characters with fourth wall awareness. He has the ability to hear non-diegetic sounds and picked up on Coach Gills' internal narrations multiple times.