The term "persons" narrows this down quite a bit. Aedra, daedra, personifications and such don't count, I take it?
1. Kagnerac, pretty much the best ever to craft with his hands and magicka.
2. Vivec, pretty much the best ever to cause mind[censored] with his brain and pen.
3. Sheogorath. Lives an easy eternal life as part of a genius cycle of replacing himself from time to time. Very smart way to live. No stress. Kind of "a person"; worsened Daedra Lord who once was a mortal?
4. Vanus Galerion, a great mystic who seemed to be smart to know the pleasant boundaries of his craft. Didn't die a sudden death while seeking power like Mannimarco, Jagar and some folks mentioned here - they were not as smart!
5. A Guy Who Has Read Most Elder Scrolls, Retained Eyesight, And Interpreted The Scrolls Most Right.
If Fyr was so smart he should have known parading around in the only full set of Daedric armor was a bad idea.
So should have the player character! Maybe Fyr just didn't notice he became older, weaker and more rusty a battler in a flick of an eye few hundred years.
Besides, there's always a bigger fish, so watch out, Tharkin-the-Nerevarine-wearing-that-armor!