Jack Powers (John Power) (1827 – November 1860) was an Irish born immigrant to New York, who became a soldier in the Mexican American War in California. Following his discharge he became a forty-niner, a noted gambler and horseman; but later in secret, an outlaw, highway-robber, gang leader, and murderer in southern and central California during the Gold Rush era. For a time in the 1850s, robberies and murders committed by his group of bandits made the stretch of El Camino Real through San Luis Obispo County and Santa Barbara County, making it the most dangerous route in the state, and he and his gang had almost complete control of the small city of Santa Barbara. He was eventually driven out of town, but only after intimidating and defeating the sheriff and a posse of 200. He eventually fled the state in 1858, when his role as bandit leader was exposed, and after a brief career running a ranch in the Mexican state of Sonora, he was murdered in a fight over a woman, and his body was fed to a pen of starving pigs.
Born in Ireland as John Power, he came to the United States with his parents in 1836, and settled with them in New York City. While there he learned gambling, courtly manners, and how to ride a horse; he also made the acquaintance of many street toughs in the run-down districts of the Bowery and Hell's Kitchen. When the Mexican-American War commenced in 1846, he joined the 1st Regiment of New York Volunteers with many of his friends from the streets of New York, and went west to be a soldier. The New York Volunteers was a unit organized by Colonel Jonathan D. Stevenson to occupy and settle California, and men in the unit were promised land in the region should the war be successful.