René Descartes

The guy who doubted literally everything and somehow built an entire philosophy from it. Descartes locked himself in a room with a stove (for warmth, not cooking) and decided to doubt EVERYTHING - his senses, his body, even mathematics. Evil demon controlling your thoughts? Can't rule it out! But then he realized: even if he's being deceived, something must be doing the thinking. Boom: 'I think, therefore I am.' From this one certainty, he rebuilt knowledge like a philosophical LEGO set. He also invented coordinate geometry (those x-y axes you hated in school? Thank him). Legend says his best ideas came to him in bed - he was a chronic late sleeper who did his best thinking under the covers. Living the dream, literally.