Jack "Manassa Mauler" Dempsey (June 24, 1895 – May 31, 1983) was an American boxer who held the world heavyweight title from 1919 to 1926. Dempsey's aggressive style and punching power made him one of the most popular boxers in history. Many of his fights set financial and attendance records. He is listed #7 on Ring Magazine's list of 100 greatest punchers of all time.

Born in Manassa, Colorado, with the name of William Harrison Dempsey, he grew up in a poor family of mixed ancestry. According to a January 11, 1955 Sports Illustrated article, his father, Hiram Dempsey, was Irish with a touch of Choctaw. Dempsey's mother, Celia Smoot, was English with a little Cherokee. Both parents became Mormon converts. Because his father had difficulty finding work, the family traveled often. He dropped out of grade school to work. Dempsey left home at the age of 16, eager to start a better life for himself. Due to his poverty, he frequently had to travel underneath trains and sleep in hobo camps. However, Dempsey was a strong, powerful youth who quickly discovered he had a talent for fighting. With the help of his older brother Bernie Dempsey, he began training to be a professional boxer. His other brother, John Dempsey, shot his own wife, then killed himself in a murder-suicide in 1927.

Desperate for money, Dempsey would occasionally go into saloons and challenge for fights saying "I can't sing and I can't dance, but I can lick any SOB in the house." If anyone accepted his challenge, bets would be wagered. According to Dempsey's autobiography, he rarely lost these barroom brawls.