Bruce lee's base was Wing Chun Gung fu, but near the end, the standup he practiced was basically boxing.

In the late 60s, Lee p!$$ed off a lot of practitioners of Eastern traditional martial arts by saying if you matched a top karate or gung fu man against a top boxer where the karate/gung fu guy could use all his techniques but the boxer would stick to his hands, Lee said the Boxer would come out on top because the boxers were in better physical condition and were accustomed to getting hit, and they had real fighting experience and practical techniques.