Michael Jordan, twice. First - he and his buddy played through us at Shadow Creek in Vegas, in the process we played a couple holes together. He was a little evasive up front, but after the first green we were on together then he was very nice and talkative. The next hole and a half was really interesting, we talked college basketball a little bit, and we caught up with him afterwards where he continued to be warm and even signed a couple items. This was about 6-7 years ago.
Then caught up with him again a couple years ago in Louisville at the Ryder Cup, he was the exact same way. Not very interested at the intro, but after talking about our golf/Vegas encounter he warmed up again.
Basically, he is just the freakin man - and he's cool as they come, just as you would imagine.