Thomas Horn, Jr. (November 21, 1860 – November 20, 1903) was an American Old West scout, who carried out various lines of work, including hired gunman, detective, cowboy, and soldier. He is believed to have committed 17 killings throughout the West as a hired gunman. In 1902 Horn was convicted of the murder of 14-year-old Willie Nickell near Iron Mountain, Wyoming, for which crime he was hanged.