Gareth Keenan is a fictional paper salesman on BBC's comedy The Office. He is portrayed in the series by Mackenzie Crook as a gaunt, self-important "team leader" proud of his lieutenant status in the Territorial Army, who spends his days annoying his co-workers at Wernham Hogg with his steadfast enforcement of the rules and sucking up to boss David Brent, whom he views as a mate, though Brent often acts otherwise and corrects Keenan when he omits the "to the" in his job title: "Assistant to the Regional Manager". Keenan is, essentially, a pedantic, humourless and pompous jobsworth.

His counterpart on the U.S. series is Dwight Schrute. Gareth flaunts his "team leader" status despite deskmate Tim Canterbury pointing out that it's a meaningless job title entailing more responsibility for the same pay, he takes it very seriously. His attempts to throw his inflated sense of authority around the office rarely work, and it is clear that no one pays any attention to him.

Tim plays endless pranks on Gareth, such as hiding his computer, putting his stapler in jelly (a prank that has been reprised in several other versions of The Office, including the US version), gluing his phone so that the receiver cannot be picked up (and then phoning him up) and playing on Gareth's naïveté by encouraging him to discuss warfare with language which could be interpreted as being homosexual in nature (e.g. 'the enemy has discovered your camp...and they've all entered your hole', 'taking a man from behind' or 'could you give a man a lethal blow?' could be interpreted in different ways) as well as (in the Christmas special) distracting Gareth while stealing his keys and then locking him in his office. Gareth says "He's done it again!", showing that Tim does this practical joke repeatedly. Gareth has mentioned in one of the early episodes that his compact disc collection includes George Michael, Queen and the Pet Shop Boys (all mentioned to disprove accusations of homophobia, pointing out "they're all bummers").

His favourite band is Mike and the Mechanics.

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