Complex sentence: He was the world middleweight champion between October 1953 and December 1955, the longest reign of any champion in that division during the 1950s, although he is probably best remembered for his three knockout defeats at the hands of Sugar Ray Robinson.
Split into simpler sentences: He was the world middleweight champion between October 1953 and December 1955, the longest reign of any champion in that division during the 1950s. Although he is probably best remembered for his three knockout defeats against Sugar Ray Robinson.