Jack Johnson won the lineal heavyweight championship by knocking out Jim Jeffries. The racism was so bad at the time that the police stopped the fight just as Jeffries was going down. To this day there is no footage of the official knockout.
July 4, 1919
Jack Dempsey destroyed the giant 6’6 monster Jess Willard to win the heavyweight championship. Jess was the favorite going into the fight and had previously killed an opponent in the ring. But in the first round, Jack dropped Jess with an explosive left hook that broke his jaw in SEVEN places.