Good martial arts film actor. Tremendous physique.
With regards to fighting skill... ehhhhh. Overrated.
Though he has been quoted to say that he thought the combination of boxing and wrestling was formidable, so it's not like he shunned the ground.
We'll never have concrete evidence of his fighting abilities. But I will say this, only someone who has actual fighting experience could come up with his revolutionary ideas. How did WE know that pure striking was not enough? UFC 1. When was that? 30 years after Bruce Lee's recognition of the need to incorporate grappling.
We also know that grappling alone isn't enough. How? A decade after UFC 1 when strikers with grappling started to dominate.
Bruce Lee figured out all of that because he sparred and fought realistically with his students and training partners. And when you do that, you inevitably see what works and what doesn't. And while his SKILL may not match the top fighters today, his mindset, his training philosophy was decades ahead of his time.
Even his sparring gloves are the forerunners of the modern MMA glove. His custom made gloves had individual fingers so that he could use his fingers/hands to grapple and trap.
Only in the last few years do you see armbars and grappling moves in fight scenes in TVs and movies. Bruce Lee? Been there and done that 30 years ago.
I have no doubt that Bruce Lee, had there been a UFC arena in his time, would have owned everyone just like Royce did 30 years later.