He started out as a street fighter in Hong Kong.
I remember seeing an interview with a bunch of Hollywood types, a few stars etc, that had gone to Hong Kong with Bruce Lee. While walking down the street he was challenged to numerous street fights, just in a few blocks (I lived in Hong Kong for most of 1996 before the Chinese took it back, and it was the same then as in Bruce Lee's time, stamping your foot on the ground meant you wanted to throw down). Bruce Lee took EVERY fight, much to the shock and horror or the Hollywooders, and he beat the living hell out of all comers, a few of them in 2 or even 3 on one fights. The witnesses said these were savage, horrific fights, not the scripted movie things that Bruce Lee is most known for. Ground fighting or not, pretty amazing to have several fights in a short time and space, and win them all. Also, the Governator has always maintained that Bruce Lee was pound for pound the strongest man in living history, and if you do a bit of research on what he was capable of, anyone would have to agree.
The Undertaker...I still can't stop laughing. For once Karaya and I agree 100%, I never thought the day would arrive. Bruce Lee would KILL the Undertaker and then beat the life out of his entourage.