The term gunslinger is a modern, 20th-century invention, often used in cinema or other media to refer to men in the American Old West who had gained a reputation as being dangerous with a gun.
An outlaw had usually been convicted of a crime, such as Black Bart, but may have only gained a reputation as operating outside the law, such as Ike Clanton.
Some crimes were carried out by Mexicans and Native Americans against white citizens who were targets of opportunity along the U.S.–Mexico border, particularly in Texas, New Mexico, Arizona, and California.
Marshal Virgil Earp and Cochise County, Arizona Sheriff Johnny Behan.
When an outlaw committed a crime, the local sheriff or marshal would usually form a posse to attempt to capture them.