The Fitzsimmons-Maher Prizefight (February 21, 1896), also considered, unofficially, as the 1896 World Heavyweight Championship, occurred between Bob Fitzsimmons and Peter Maher on a sandbar in the Rio Grande River just far enough outside of the American city of Langtry, Texas, in which state boxing was illegal, to be considered technically in the Mexican state of Coahuila de Zaragoza. Fitzsimmons was victorious, knocking Maher out in the first round; however, upon hearing of the outcome of the fight, the 1895 World Heavyweight Champion James J. Corbett immediately rescinded his retirement.

Robert James Fitzsimmons (26 May 1863 – 22 October 1917) was a British professional boxer who was the sport's first three-division world champion. He also achieved fame for beating Gentleman Jim Corbett (the man who beat John L. Sullivan), and he is in The Guinness Book of World Records as the lightest heavyweight champion, weighing just 165 pounds when he won the title. Nicknamed Ruby Robert and The Freckled Wonder, he took pride in his lack of scars and appeared in the ring wearing heavy woollen underwear to conceal the disparity between his trunk and leg-development.

Considered one of the hardest punchers in boxing history, Fitzsimmons is ranked as No. 8 on The Ring magazine's list of 100 greatest punchers of all time.