Albert "Swejen" Swearengen (Ian McShane), is the proprietor of the Gem Saloon, born in England but raised in a Chicago orphanage under an abusive figure known as Mrs. Anderson. He mentions on occasion that Mrs. Anderson ran a brothel at the girls' orphanage before running the boys' orphanage. Swearengen was among the first settlers of Deadwood, earning him several land claims and a position of power. The Gem Saloon, offering alcohol, prostitution and faro also acts as Swearengen’s base of operations.

Swearengen is cunning, manipulative and initially appears to be the most cynically amoral of all the characters, showing no hesitation in resorting to violence and murder when it serves his business interests. When former Montana marshal Seth Bullock comes to camp to sell hardware, his upright, law-abiding manner and strong sense of justice serves as an unintended, yet upending threat to Swearengen, and they initially butt heads until Swearengen decides to make Bullock the "face" of Deadwood and encourages him to pick up the badge again, turning Bullock's respectability to his advantage in securing the future of the camp.

Swearengen’s central goal is to retain his own business interests in Deadwood and keep the camp stable and secure in order to get the territory annexed by the United States. As the camp is set upon, first by political interests and then by big capital, Swearengen comes to the realization that the preservation of his own interests depends on collaboration with others in the camp.

While his alliances are often pragmatic and self-serving, Swearengen does show great loyalty to allies such as Mr. Wu. He displays an almost paternalistic (though often abusive) affection for his three main henchmen, Dan Dority, Johnny Burns, and Silas Adams. He is affectionate toward Trixie, one of the prostitutes of the Gem, and is deeply offended when she begins a relationship with Sol Star.

Though he is portrayed as a cutthroat criminal, his character is shown to be more complex, motivated by a peculiar type of morality and justice as well as a need to protect the vulnerable even while seeming to disparage them. For example, though he professes to keep the crippled Jewel around in case someone with only nine cents wants a prostitute, Trixie relates that his employment of Jewel is really his 'sick way' of protecting her. Swearengen smothers the Rev. Smith, but this was to end his suffering rather than out of ill intent.[1] In season 3 he murders an agent of George Hearst for shooting at Alma Garret, beating A.W Merrick, and humiliating Wu. His opposition to both the Pinkertons and George Hearst's machinations also demonstrate a character motivated by morality and the desire to protect the powerless. This is strongly contrasted with his rival Cy Tolliver, who shows little compassion or motivation beyond pure self-interest. Al is thus portrayed as a more heroic character as the series progresses, while Cy remains a villain.

The character is based on the real-life Al Swearengen, who owned the Gem Theater in Deadwood. Unlike the character, the historical Al Swearengen was not English and was born in Iowa.[2]

Ian McShane won a Golden Globe in 2005 for his portrayal of Swearengen.