Maxperson
Morkus from Orkus
Morgoth also gets defeated multiple times.I never saw Sauron as particularly smart. More like tough to kill with a limitless army. He gets defeated multiple times, and his hubris and evil gives him such a giant blindspot (complete inability to think anyone would want to destroy the Ring) that leads to his ultimate defeat. I can't think of anything he did in LotR that was really clever.
The thing with Sauron is that he is like Saruman. He was a very skill maker who worked directly under Aule and was that valar's mightiest maia. Knowledge and crafting were his thing. He may not have been Einstein, but he was smart enough to be able to help the elves craft artifacts.
Initially Sauron was a spy for Morgoth who fed him information on what the Valar were doing. You don't make dumb people spies and you don't go undiscovered if you aren't pretty crafty.