Ellis Alfred Swearengen (July 8, 1845 – November 15, 1904) was an American pimp and entertainment entrepreneur who ran the Gem Theater, a notorious brothel, in Deadwood, South Dakota, for 22 years during the late 19th century.

As stated in the 1882 New Year Edition of the Black Hills Pioneer, which described the early history of Custer, "Al Swearengen was running a dance house of 30X150 feet in dimensions and day and night a man had to push and crowd to get into it."

[8] Swearengen's talent for making canny alliances and financial payoffs kept him insulated from the general drive to clean up Deadwood, including the otherwise successful work of Seth Bullock, the town's first sheriff.

According to his rediscovered obituary and contemporaneous newspaper accounts, Swearengen was found dead in the middle of a suburban Denver street on November 15, 1904, apparently of a massive head wound.

[10] From 2004 to 2006, the television series Deadwood depicted Swearengen as a powerful and influential figure in the early history of the town, ruthlessly murderous and abusive, but ultimately guiding it toward its development and annexation to the Dakota Territory once he comes to see this course as fitting his best interests.