I met Johnny Bench after a Bisons game at War Memorial in 1967. He had the dimensions of a brick.
I met OJ in Lockport Memorial Hospital, where my mother worked. He used to visit kids in hospitals around the area. He was so ridiculously athletic that he seemed to float, not walk, through the halls.
(I've met a few more, but I'll confine my response to GOATs and HOFers.)