Harry Alonzo Longabaugh, better known as the Sundance Kid, was an outlaw and member of Butch Cassidy's Wild Bunch in the American Old West. He likely met Butch Cassidy during a hunting trip in 1883 or earlier. The "Wild Bunch" gang performed the longest string of successful train and bank robberies in American history.

Butch Cassidy's Wild Bunch was one of the loosely organized outlaw gangs operating out of the Hole-in-the-Wall, near Kaycee in Wyoming, a natural fortress of caves, with a narrow entrance that was constantly guarded. In the beginning, the gang was referred to as the "Hole in the Wall Gang" during the Old West era in the United States. It was popularized by the 1969 movie, Butch Cassidy and the Sundance Kid, and took its name from the original Wild Bunch. The gang was led by Butch Cassidy, and it included his closest friends Elzy Lay, the Sundance Kid, Tall Texan, News Carver, Camilla "Deaf Charley" Hanks, Laura Bullion, Flat-Nose Curry, Kid Curry, and Bob Meeks. They were the most successful train-robbing gang in history.