If you mean strength as in muscles and lifting shit, he was really strong for someone his size. He had an insane body building routine going on. If you mean in a fight, then it gets more complicated. He lived in a time where bullshit was the #1 rule in martial arts. He has a totally unsubstantiated record of wins peppered in with a few verified fights.
Overall, the impression he left was that he was genuinely interested in always striving to become a better martial artist. He very rapidly understood that his background in traditional chinese martial arts would leave him absolutely expose and he cross trained with Judo and boxing experts. However, there is no evidence that he actually took to any of these cross-disciplines.
He was also way, way smaller than most of the legit fighters of his era. He would not have lasted more than a few minutes with Judo Gene, or Karl Gotch or Inoki. He would have been a similar size with a few of the second generation Gracies, but then again, no way he would last against their heavy Vale Tudo inspired style.
