9. Philip Davidson
Naturally, when you think of the smartest characters in the history of Brooklyn Nine-Nine, your mind automatically goes to the detectives of the titular precinct. They are the stars of the show, but wouldn't have too tough of a job if they weren't coming up against equally smart criminals.
Philip Davidson was one of the most intelligent killers either Jake Peralta or Captain Holt ever came up against. In Season 5's episode The Box, Davidson was accused of murdering his business partner, but had an answer for everything Jake and Holt threw at him.
His alibi was water tight, and his story was as straight as could possibly be. Every move he made whilst committing the crime was calculated to be explained away, and the plan worked perfectly, until Jake accused him of being lucky.
Davidson's downfall was not his intelligence, but his pride. He needed to boast about just how smart he was, and couldn't stand the thought of people thinking he got away with murder by accident. If he could have gone just fourteen more minutes without snapping, he would have gotten away with murder, but he was just too proud of himself.