Jack Dempsey was born on June 24, 1895 in Manassa, Colorado. He was raised in a poor family and had to travel around the country with his family to find work for his father. He dropped out of grade school to find work for himself. Dempsey moved out at age 16 ready to make a better life for himself. He frequently had to sleep in homeless camps and travel underneath trains because he had very little money. Jack as strong and powerful and discovered that he was good at fighting. He would go into bars to pick fights to earn a little money.
He would say "I can't sing and I can't dance ,but I can lick any SOB in this house." If people accepted his challenge they would wager against who would win. Dempsey's boxing recorded is not know, because he had a couple of names he went by when he boxed. He went by Kid Blackie which he used till 1916. He first appeared as Jack Dempsey in 1914 as a middleweight boxer. While the United States went in WW1 Dempsey worked at a shipyard and even enlisted in the army but was turned down. Jack was the heavyweight champion of the world from 1919-1926. He held that tittle for 5 years till Gene Tunney.
http://en.wikipedia.org/wiki/Jack_Dempsey
http://www.biography.com/people/jack-dempsey-9271466