Brian Nielsen (born 1 April 1965) is a Danish former professional boxer. He held the IBO heavyweight title from 1996 to 1999 successfully defending it five times, including against Larry Holmes and Phil Jackson, the second highest number of defenses behind Wladimir Klitschko's record of 18. At one point of time, he equaled Rocky Marciano's record of 49 successive wins with no losses. While he never held a world title from any of the main four sanctioning bodies (WBC, IBF, WBA, WBO), he did defeat several former world champions who had, including Orlin Norris, Carlos De León, Jeff Lampkin, and Tony Tubbs. As an amateur, Nielsen won bronze medals in the super heavyweight division at the 1991 European Championships and the 1992 Olympics in Barcelona.

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