Capt. "Mister Nasty" Thaddeus Harris of the police academy, he always attempts to discredit Lassard and his men, but ends up being the butt of most of the jokes. Starting with Police Academy 4, he inherits Proctor from Mauser. He generally seems to be success-driven, at the cost of Lassard and his men. Started as Lieutenant in the first film but is promoted to Captain in other films to come. His catchphrase is: "Move it! Move it! Move it!" He is also deathly afraid of heights, as evidenced in an undercover stakeout in the sixth film, in which his and Proctor's covers are window washers for a high-rise office tower. He derives pleasure from tormenting and belittling his subordinates - first the cadets he instructs at the academy, then Lassard's men whom he outranks. Although he is generally disliked by his colleagues because of his treatment of them, those same people end up rescuing him.
Despite his role as antagonist, some scenes display Harris's genuine desire to see graduates become good cops. His initial dislike of Mahoney is based in part on his belief that he is disrupting the development of people, "who might make pretty good police officers". He heavily favors Blankes and Copeland and recruits them as squad leaders. Later, in the seventh movie, Harris and the rest of the team develop a 'peace' of sorts, with Harris joining them in the rescue attempt of Callahan and providing the team with the necessary equipment to track the criminals. He even demonstrates trust in Tackleberry by requesting he be the one to shoot a locator bullet into the bad guy's car, notably calling him by his nickname "Tack" when doing so.
He works with Proctor in the fourth, fifth, and sixth films and the animated series. In the animated series Captain Harris is portrayed as gruff but not as sadistic as he was in the movies, and generally more competent. He also seems to take out his dislike of Mahoney through red tape rather than direct action. When Captain Harris was tasked with investigating a string of crimes at the beach, he is also responsible for getting all the officers undercover assignments, to which Mahoney and Jones are assigned to be sanitation workers picking up litter. While Jones accepts his assignment, Mahoney complains that Harris gave them this work to express his dislike of them. A reformed Mauser defends Mahoney and confronts Harris for his actions. He then belittles Harris for taking out his anger on his former cadets out of convenience, rather than disciplinary purposes.
In the animated series episode Police Academy Blues, Harris finally achieves his long-awaited dream of becoming Commandant when Lassard is forced to step down, due to the Professor's Supercar being stolen under Lassard's watch. However, Commandant Harris's crowning moment is short-lived, as Mahoney and crew track down and capture the Supercar robbers, ensuring Lassard's reinstatement as Commandant, and Harris's demotion to the rank of Captain once again.