Most of the characters (Seth Bullock, Al Swearengen, Sol Star, Reverend Smith, the Metz family, et cetera, in addition to the more famous Wild Bill Hickock, Calamity Jane, and Jack McCall), have real-life counterparts.
Powers Boothe was originally cast as Al Swearengen. But Boothe fell ill before the pilot was to start filming. Boothe was replaced by Ian McShane, and then was given the supporting role of Cy Tolliver.
A feature film based on the series has been rumored for many years, but the cast has cited the difficulties of coordinating the schedules of everybody involved as a main obstacle. In 2016, HBO head Mike Lombardo said David Milch had pitched a general script, and that the network is fully committed to the movie.
David Milch originally created the role of Al Swearengen specifically for Ed O'Neill. O'Neill screen-tested for the role, but HBO executives did not want to cast him, because of his fame as Al Bundy from Married... with Children (1987). After Deadwood was canceled, Ed O'Neill was cast in David Milch's next project, John from Cincinnati (2007).
George Hearst was the father of William Randolph Hearst, the famous newspaperman on whom Citizen Kane (1941) was based, and the great-grandfather of Patricia Hearst. When Hearst tells Merrick that he will start his own newspaper in Deadwood to tell lies for his side, it is a reference to the fact that W. R. Hearst is largely credited with the creation of the concept of "yellow journalism", and the use of his own newspapers to shape, and even create political and social opinion and actual events. The most famous example of this was what many historians characterize as W. R. Hearst's whole cloth creation of the Spanish-American War through his newspapers' inflammatory and lucrative headlines.
The show's cancellation was a shock to the cast. During the third season, Timothy Olyphant and Ian McShane successfully renegotiated their contracts for higher pay, and HBO retroactively paid them the increased rate for the nine episodes of the season already shot. The show was cancelled a few weeks later.
Until the end of season two, the character of Ellsworth did not have a first name. When it was decided to give him a first name, the actor portraying the role, Jim Beaver, requested that he be given the first name Whitney, after Whitney Ellsworth, Producer of Adventures of Superman (1952), whom Beaver knew from his research for a book on the life of "Superman" star George Reeves.
Garret Dillahunt pursued the role of Seth Bullock, but Timothy Olyphant was already cast. The only role that was available at the time, was of Doc Cochran, so Dillahunt auditioned for that. He played the recurring role of Jack McCall in season one. Dillahunt was then considered for the role of George Hearst in season two, but it was decided that Hearst would not appear on-screen until the season finale. Dillahunt played the recurring role of Hearst's employee, Francis Wolcott.
Keith Carradine was grateful that he had time to grow a real mustache for his role as Wild Bill Hickok, thus sparing him the hassle of gluing on a fake one every day. However, he did have to wear blue contact lenses to simulate Hickok's eye color. Ultimately this helped his performance. The contacts hurt his eyes, and helped him achieve Hickok's perpetual foul mood.
Over the course of the series several actors originally hired as extras were given recurring speaking roles. This stemmed in part from David Milch's habit of rewriting scenes on the fly during production. He would decide on set that a line of dialogue was needed and then assign it to one of background actors who was already there. If he liked their performance, the character would get more scenes in subsequent episodes.
David Milch had originally planned to write a series set in Ancient Rome, telling the story of a society amid the development of law and order. However, when he approached HBO, he was informed of the series Rome (2005) that was then in development. He took the suggestion to change the setting and created a Western using the same themes instead.
According to a 2004 Jewish Journal of Greater Los Angeles interview with show creator David Milch, when John Hawkes first met Milch to audition for the role of Sol Star, Hawkes told Milch that he was not actually Jewish (unlike both the real-life Star and the "Deadwood" character). Milch's response was to ask Hawkes, "Have you ever felt shame or sadness or ostracized?" When Hawkes responded, "Every day". Milch told him, "Then you're Jewish."
HBO offered the chance to David Milch to wrap the series in a shorter fourth season, but he declined to do it on those conditions. However, when Chris Albrecht was asked about it, he said that they also told Milch that HBO would give him a full twelve-episode season, if it was what he needed to wrap the show. Milch told them he would think about it over a weekend, but the news about the show possibly being cancelled reached the press to such a speed, that that conversation never happened, and Milch just moved on to develop John from Cincinnati (2007).
Despite appearing in thirty-two out of thirty-six episodes, Jeffrey Jones (Merrick) was listed as a guest star in the first season. Similarly, Gerald McRaney (George Hurst) received a "special guest star" credit in season three, even though he appeared in all twelve episodes of that season.
Throughout the series Al makes disparaging references to the town of Yankton. As the territorial capital of the Dakota Territory from 1861 to 1889, Yankton was one of the few outposts of government authority in the region.
Robin Weigert, who had been primarily a theater actress before landing the series, rented a professional cowgirl outfit she couldn't afford for her final audition in Los Angeles, to make her feel more like Calamity Jane. After walking across the Avenue of the Stars in Los Angeles in full cowgirl regalia, she impressed the executives and won the part. She flew back to New York on the same flight as David Milch, who requested to change seats so he could sit next to her and tell her stories.
David Milch told Robin Weigert to ignore established folklore of Calamity Jane, including her own stories, since Jane had been known to embellish greatly. Weigert, however, received "generous help" from actress Jane Alexander, who had portrayed her in Calamity Jane (1984). Alexander had interviewed a centenarian who as a young boy had mended fences for the real Calamity Jane before her death in 1903.
The opening credit sequence featuring a riderless horse running through Deadwood was conceived and shot by producer Davis Guggenheim. The woman lowering herself into the tub is actress Bethalyn Staples, who had a small role in the series as one of the Bella Union saloon girls.
Certain actors and actresses that were eventually cast in the series, initially auditioned for different roles. For example, Paula Malcomson (Trixie) initially auditioned to play Alma Garrett and W. Earl Brown (Dan Dority) pursued the role of Jack McCall.
According to Robin Weigert, when she was shooting a scene between Calamity Jane and Alma Garrett (played by Molly Parker) series creator David Milch commented that it was if a character from Mark Twain met a character from Henry James, and the two were forced to have a conversation.
David Milch altered Al Swearengen's background after casting British actor Ian McShane, who was born and raised in Lancashire, England. The real Swearengen was born and raised in Chicago, of Dutch heritage, but Milch changed it so Al was born in England before moving to Chicago as a boy, as "insurance" in case fans heard hints of McShane's English accent at any point.
The cemetery depicted in the series is a grossly inaccurate geographical location. The Mt Moriah Cemetery overlooks the town of Deadwood and has the tombs of Bill Hickok, Calamity Jane, and Seth Bullock, among others.
In her first audition for Calamity Jane, Robin Weigert did her best performance to depict Jane as a tough, scary woman. She was told the producers "loved the vulnerability" she showed as Jane, but they wanted to see her again doing the role a bit more tough and intimidating.
Actress Geri Jewell was written into the series after a chance encounter with creator David Milch at a pharmacy in Santa Monica, when he was first developing the show. She didn't recognize him and thought he was crazy at first when he wrote his phone number down on an antidepressant ad from the pharmacy counter.
Several of Deadwood's main cast would go on to be regulars on Fear The Walking Dead: Kim Dickens (Joanie Stubbs/Madison Clark), Dayton Callie (Charlie Utter/Jeremiah Otto), and Garret Dillahunt (Francis Wolcott, Jack McCall/John Dorie); (DW/FTWD respectively).
Alice in Chains guitarist/vocalist Jerry Cantrell gave W. Earl Brown (Dan Dority) the idea on how to end the fight between Dan and Captain Turner on season 3 episode 5, "A Two-Headed Beast". It was based on a fight that Cantrell's younger brother, David was involved in a biker bar in Oklahoma.
Several times throughout the series, characters reference a financial scandal of some sort out east which has some folks reticent to invest in new ventures. This is likely a reference to the Credit Mobilier scandal in 1872. It was revealed that several high ranking members of the Union Pacific Railroad had set up a phony construction company (Credit Mobilier) that had bilked 23 million dollars out of investors and the federal government. The scandal included several sitting congressmen as will as the vice president, and many investors lost everything.
The trivia items below may give away important plot points.
The series shows Seth Bullock and Sol Star witness Wild Bill Hickok's arrival in Deadwood. However, in reality, Wild Bill arrived in Deadwood two weeks prior to Bullock. Bullock arrived in Deadwood on August 1, 1876, the day before Bill was killed by Jack McCall.
Gerald McRaney (George Hearst) also appeared in Timothy Olyphant's (Seth Bullock) other TV show Justified (2010). And, Gerald McRaney and Cleo King (Hearst's Aunt Lou) in season 3. Both of them appeared on Mike&Molly (2010) Mike & Molly (2010). He played Mike's Captain Murphy, and dated Mike's mom on 6 episodes. She appeared as Carl's nana.