James "Jem" Mace (8 April 1831 – 30 November 1910) was an English boxing champion, primarily during the bare-knuckle era. He was born at Beeston, Norfolk. Although nicknamed "The Gypsy", he denied Romani ethnicity in his autobiography. Fighting in England, at the height of his career between 1860 and 1866, he won the English Welterweight, Heavyweight, and Middleweight Championships and was considered one of the most scientific boxers of the era. Most impressively, he held the World Heavyweight Championship from 1870 to 1871 while fighting in the United States.