Born around 1854, Middleton arrived in Lincoln County, New Mexico, from Texas in the mid-1870s. Described as a heavyset, swarthy man with black hair and eyes and a large handlebar mustache, Middleton was known as a first-rate cowboy and an excellent fistfighter and pistol marksman.
Upon his arrival in New Mexico, he went to work as a cowboy for John Tunstall. When Tunstall and Alexander McSween, got into a feud with the Dolan-Murphy faction of Lincoln, New Mexico, Middleton obviously sided with Tunstall. After Tunstall was killed, Richard Brewer was appointed as town constable and put together a group known as “The Regulators,” including Middleton, Billy the Kid, and other deputies.
As the Lincoln County War erupted, Middleton utilized his excellent shooting skills to participate in many battles. On April 4, 1878, he was seriously wounded in the chest during a gunfight with Buckshot Roberts at Blazer’s Mill. When the “war” was finally over, the Regulators split up.
Where he went is in dispute. Some say that he remained in the area, dying of smallpox on November 18, 1882. Other accounts say he moved to Kansas, where he married and worked as a cowboy, dying in 1885. However, popular evidence shows that he wound up getting involved with his cousin Jim Reed and his wife Belle Starr, getting in further trouble with the law before being found face down in the mud of the Poteau River near the Arkansas border in May of 1885.