Definitely gotta start with Sherlock Holmes. Arthur Conan Doyle just nailed that specific type of brilliance that borders on the obnoxious, you know? The violin playing, the cocaine use, the whole 'deduction from a speck of mud' thing. He's the template. But for pure character work, I'm way more drawn to someone like Inspector Morse from Colin Dexter's series. He's melancholic, loves opera and real ale, gets things wrong sometimes. His intelligence is quieter, more human, and wrapped in this lovely, grumpy vulnerability. The TV adaptation with John Thaw perfected that tone.
Then you have the modern giants. Harry Hole from Jo Nesbø's books is a classic Scandinavian mess—alcoholic, self-destructive, but with a relentless moral compass buried under all the damage. His iconic trait is basically his ability to survive his own worst impulses while solving horrific crimes. It's a different kind of 'brilliance' altogether, one born from pain rather than cold logic.