Alexander McSween (c. 1843 – July 19, 1878) was a prominent figure during the Lincoln County War of the Old West, and a central character, alongside John Tunstall, in opposing businessmen and gunmen Lawrence Murphy and James Dolan.
Born Alexander Anderson McSween, in Canada, McSween was for a time in his youth a preacher. Afterwards he attended law school for one year, in St. Louis, Missouri before moving to Kansas, then to New Mexico Territory. He had married Susan Hummer in 1873. After he arrived in Lincoln County, New Mexico, McSween worked for Murphy-Dolan as an attorney, then left them to work for John Tunstall, with whom he became close friends and by 1876, business partners.
When the trouble between the two factions began, Murphy-Dolan accused McSween of embezzlement, and they hired gunmen from the Evans and Kinney gangs to rustle Tunstall's cattle and harass him. McSween-Tunstall hired gunmen to protect them and their properties, including Billy the Kid, Dick Brewer, George Coe, and Frank Coe, among others. On February 18, 1878, Tunstall was murdered by William Morton, Jesse Evans and Tom Hill.