Met quite a few, but the one worth mentioning was mother teresa, at mother house in Calcutta. Worked in one of her missions back in 95.
Didn't seek to meet her, but was my first day of volunteering so had asked others when and where they met (to then go to work), to my shock they said 6am (work started at 8am) outside the salvation army hostel, I wouldn't have met them had I known they were going that early as they were all Catholics and it was sunday so they were going to mass at mother house first (Duh, go figure!). So we went to the mass (although I considered myself an atheist at that time) and the mother gave part of it, then they announced that they had a couple of Australian preachers of the calendar method after mass they would like us to hear, at that point I thought 'I'm not interested in this and am really nervous about working, I'll go out and have a fag whilst they do this talk' so I got up and left and she was standing in the doorway, I shook her hand and went completely blank (what do you say?).
It was one of the best days of my life, not really meeting her per se, but phoning home and telling my mum I was working there and met her (it wasn't planned, I just met some folks who worked there when I was on my way to Thailand, then on the way back thought, I'm going to volunteer it seemed like a cool thing to do).
Met her again when I was forced to register (as I hadn't, didn't know I needed to), but this time she was surrounded by other volunteers and I just hung back and let them have their moment/time with her.
She was very very small and wrinkly, but had a presence I've never encountered before or since (though maybe that was just my perception rather than anything real).