William's son, Andrew, operates a lawn-and-gutter service in Raleigh, N.C., called The Blade Runner.
As a boy growing up in Memphis, Tennessee, Sanderson delivered The Commercial Appeal newspaper, played youth baseball, and attended Bellevue Baptist Church.
Sanderson received a Distinguished Alumnus award from the University of Memphis in 2008.
William and his wife, Sharon, have homes in Burbank, California and Harisburg, Pennsylvania.
Cracked magazine named William Sanderson one of its "15 Funniest People of 2006," for his comedic portrayal of E.B. Farnum on Deadwood.
Sanderson has appeared in Los Angeles in plays such as "Authentic Life of Billy the Kid" (Directed by Tommy Lee Jones), "Tobacco Road," "Scotch Rocks," and "Ground Zero."
Sanderson has appeared in the following productions on the New York stage: "To Kill a Mocking Bird," "Hello Out There," "When You Comin' Back Red Ryder," and "The Taming of the Shrew," as well as other shows.
While a teenager William used his ability to portray different characters to sneak into concerts and sporting events for free.
Sanderson has played the "sleazy" character in so many westerns that he says his specialty is playing "prairie scum."
Sanderson has appeared in many westerns, such as "Last Man Standing," with Bruce Willis, "Lonesome Dove," with Robert Duvall, "Monte Walsh," with Tom Selleck, and most recently in HBO's "Deadwood."
Sanderson's role as Larry, along with his brother Darryl and his other brother Darryl, in Newhart was intended to be a one-time appearance. The characters were so well accepted they became regulars through the rest of the series' run.
William appeared in four projects with Tommy Lee Jones: "Coal Miner's Daughter," "The Client," "Lonesome Dove" and "The Executioner's Song."
While in the U.S. Army Sanderson served as a medic.
William's mother was an elementary school teacher, and his father was a landscape designer.
Sanderson appeared in two films with Sissy Spacek: as Loretta Lynn's uncle in "Coal Miner's Daughter" (1980) and as Calvin in "Raggedy Man" (1981).
Early in his acting career William appeared in over thirty off-Broadway stage productions.
After a stint in the Army, Sanderson graduated from Memphis State University and then attended its law school.
He married Sharon Wix on December 5, 1993.
William Sanderson played a part in the movie Blade Runner where he designed human-like robots. Later, he played a role in Batman: The Animated Series where his character did the same thing.
William Sanderson: (on his previous drinking problem) You know, there are actors who sit around and make themselves into outlaws. I would get the roles mixed up with myself. But nobody's been given more second chances than I have.
William Sanderson: (describing E.B. Farnum, his character on Deadwood) [He is] a sneak and a sycophant--a weasel. He's a pathetically funny character.
William Sanderson: (on hanging out with Elvis Presley while growing up in Memphis) I did some pretty dumb things to impress Elvis, like playing too rough in football or hitting his car too hard in the bumper cars at the park, but he never really got mad.
William Sanderson: (on pursuing acting after four years of college and three years of law school) Well, I think subconsciously I wanted to [act] all along. I probably was a coward. I was very shy. But also I had gone to a great school in high school. And my friends are lawyers and doctors, one of whom is one of Al Gore's lawyers. He was one of my closest friends in childhood. I got the G.I. Bill and at one point, I thought I would be a lawyer. But I never practiced. I never took the Bar. I went to New York and did theater. But I always loved movies and had a friend that did theater in high school and I would go see him, but way too scared to get on the stage.
William Sanderson: (on growing up in Memphis) Well, it was very exciting because that's where [Elvis] Presley was. Where he started. And the music was a fabulous inspiration, being able to see Johnny Cash, Jerry Lee Lewis, Roy Orbison and it just went on and on. And I also saw the African-American entertainers from Stax Records like Sam & Dave. I don't think I saw Otis Redding, but I heard him all the time. So we had that great music and acting was the closest I could get to it.
William Sanderson: It's better to be type-cast, then not cast at all.