British boxer, the first man to successfully defend an Olympic boxing title. Mallin was one of the dominant middleweight fighters of his generation. In addition to his Olympic triumphs, he won five British amateur titles and was undefeated in over 300 fights.

Mallin, a London policeman, made his first Olympic appearance at the 1920 Olympics in Antwerp, Belg. He dominated his weight class, winning the gold medal in a decision over Georges Prudhomme of Canada. In 1924 Mallin returned to the Olympics in Paris to defend his title. He became involved in one of the most controversial fights in Olympic history when he faced Frenchman Roger Brousse in a quarterfinal round. At the end of the fight, Mallin showed the Belgian referee a number of bite marks on his chest. The referee ignored him and read out the verdict, which awarded the fight to Brousse in a 2–1 decision. Although most observers felt that Mallin had dominated the fight, he declined to lodge a protest. However, a Swedish member of an international boxing association protested, and an inquiry revealed that Brousse had inflicted severe bites on Mallin's chest. Brousse was disqualified and Mallin advanced to the next round, leading to a near riot by the supporters of Brousse.

In the finals the next day, Mallin defeated fellow Briton John Elliott to successfully defend his title. The match was held in an atmosphere of turmoil, as French fight fans loudly protested the disqualification of their hometown hero. As a result of the Mallin-Brousse controversy, some observers called for an end to the Olympics, citing the nationalist tension resulting from the competition.

Mallin continued his career as a policeman following the 1924 Games. He continued to box but never turned professional. Mallin's record of over 300 fights without a loss is unsurpassed, and his skill, sportsmanship, and devotion to amateur status have been held up as one of the finest examples of the Olympic ideal.