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, Camillo "Deaf Charley" Hanks, Laura Bullion, Flat-Nose Curry, Kid Curry, and Bub Meeks.

The Wild Bunch gang claimed to make every attempt to abstain from killing people, and Cassidy boasted of having never killed a single man or woman in his entire career. These claims were false, however. Kid Curry, "Flat-Nose" Curry, Will "News" Carver, and other members of the gang killed numerous people during their flight from law enforcement. Kid Curry alone killed nine lawmen while with the gang, and another two civilians during shootouts, becoming the gang's most feared member.^{[citation needed]} Elzy Lay killed another two lawmen following a robbery, for which he was wounded, arrested, and sentenced to life imprisonment. George Curry killed at least two lawmen, before being killed by Grand County, Utah, lawmen.

The gang was also closely associated with female outlaws Ann Bassett and Josie Bassett, whose ranch near Browns Park supplied the gang often with fresh horses and beef. Both Bassett girls became romantically involved with several members of the gang, and both occasionally accompanied the gang to one of their hideouts, called "Robbers Roost". Associations with ranchers like these in the area allowed the gang considerable mobility, giving them an easy resupply of fresh horses and supplies, and a place to hole up for a night or two.

At 1:00 am on June 2, 1899, Cassidy, Sundance Kid, Harvey Logan, and Lay robbed a Union Pacific train near Wilcox, Wyoming. They wore masks made from white napkins, possibly pilfered from a Harvey House restaurant. In the holdup, they stole between $30,000 and $60,000. The gang split up afterward, a common ploy to throw off pursuers, and several fled to New Mexico. On July 11, 1899, gang members robbed a train near Folsom, New Mexico, without Cassidy's presence. The pursuit by a posse led by Sheriff Ed Farr culminated in two gun battles, during which Sheriff Farr and two deputies were killed. Gang member Sam Ketchum was wounded and died in custody. Elzy Lay, one of Cassidy's closest friends and cofounder of the Wild Bunch gang, was wounded and also captured.

Cassidy and the other members regrouped in Wyoming. On August 29, 1900, Cassidy, the Sundance Kid, Kid Curry, and another unidentified gang member believed to have been Will Carver, held up another Union Pacific train at Tipton, Wyoming. Less than a month later, on September 19, 1900, they raided the First National Bank of Winnemucca, Nevada, stealing $32,640. These and other lucrative robberies led to much notoriety and fame.

In early 1901, Cassidy, the Sundance Kid, and Sundance's girlfriend Etta Place relocated to Argentine Patagonia, where they spent time at La Leona, 110 km from El Calafate in the province of Santa Cruz, to escape the pursuit of Pinkerton detectives and other lawmen.

That same year, Will Carver was wounded by lawmen on April 1 and died in May. Ben Kilpatrick and Laura Bullion were captured in Tennessee in December 1901; he received a 20-year prison sentence and she was sentenced to five years.

Kid Curry killed two lawmen in Knoxville, Tennessee; he escaped capture and traveled to Montana, where he killed the rancher who had killed his brother Johnny years before. He was captured on his return to Tennessee, but escaped again. Kid Curry was claimed to have killed himself in Colorado in 1904 during a shootout with lawmen, for he had said that no lawman would ever take him alive.