Joseph William Calzaghe (born 23 March 1972) is a Welsh former professional boxer who competed from 1993 to 2008. He held world championships in two weight classes, including the unified World Boxing Association (WBA) Super, World Boxing Council (WBC), International Boxing Federation (IBF) and World Boxing Organization (WBO), "Ring" magazine and lineal super-middleweight titles, and the "Ring" light-heavyweight title.

Calzaghe is the longest-reigning super-middleweight world champion in boxing history, having held the WBO title for over 10 years and defending the title against 20 boxers before moving up to light-heavyweight. As his super-middleweight and light-heavyweight reigns overlapped, he retired with the longest continual time as world champion of any active boxer at the time. Calzaghe was also the first boxer to unify three of the four major world titles (WBA, WBC, and WBO) at super-middleweight, and was the first "Ring" champion in that weight class.

His unification bout with IBF super-middleweight champion Jeff Lacy on 5 March 2006 was won by an easy unanimous points decision over Lacy, who was a pre-fight favourite with the bookmakers. Calzaghe dominated throughout the fight and gained the IBF title and won every round. He also won the vacant "The Ring" and lineal titles, becoming the first super-middleweight to be recognized as world champion by "The Ring" magazine.

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