I was on a flight London to HK in First Class a few years ago (when you could still talk to other 1st Cl passengers in the aisle) and I spent some time talking to the guy behind. He was African, not so young but had a young, bejewelled glamorous wife (?) with him.
He was very friendly and unpretentious (to the point of being nice and ordinary) but changed into a suit and tie before we landed.
Surprisingly we stopped dead when taxiing into the HK airport terminal and I looked out and a staircase was being rolled up, and red carpet, line of limos and a brass band was in position- for my mate in the next seat.
The flight attendant informed me later he was the Prime Minister (or president ?) of South Africa.
Not so famous I guess (I don't even remember what his name was) but a nice brush with a famous (at the time) but humane guy.