Attended Bishop Kelly High School in Boise, Idaho. He wears his old football jersey from that school in most of his movies.
Daughter named Maite Nerea, born in 1975, in Mondragón (País Vasco, Spain).
Testified before the Senate Judiciary Committee on increased funding for crime labs.
Attended the renowned Steppenwolf Company.
In March 2002, he became engaged to his longtime girlfriend, Gina Cirone, a biology teacher. The two married in Petrignano, Italy, in 2003.
Started at Idaho State University on a football scholarship, where he found acting.
He has a production company called High Horse (with friend & fellow CSI: Crime Scene Investigation (2000) producer Cynthia Chvatal).
He has one grandchild named Mazrik William (born October 2003).
One CSI: Crime Scene Investigation (2000) plotline had him pursuing an insane killer played by Tom Noonan, who also played the titular insane killer in Manhunter (1986).
Was offered a role in Platoon (1986), but turned it down because it was a low-paying job. The prospect of going to the Philippines for weeks of training before filming did not appeal to him either.
Calls Long Gone (1987) the most fun he ever had making a movie. He made it instead of appearing in Platoon (1986).
Was cast in To Live and Die in L.A. (1985) after Gary Sinise declined the part. Sinise became the star of CSI: NY (2004), which is the spin-off of Petersen's series CSI: Crime Scene Investigation (2000).
Co-presented an award at the 2004 Emmys with Dennis Franz, whose former NYPD Blue (1993) co-star, David Caruso, stars in CSI: Miami (2002), the spin-off of Petersen's series CSI: Crime Scene Investigation (2000).
Has played two characters with the surname "Walker." He played Gideon Walker in Return to Lonesome Dove (1993) and Steve Walker in Fear (1996).
Declined the offer to produce CSI: Miami (2002), the spin-off of his series CSI: Crime Scene Investigation (2000).
Because his role in Manhunter (1986) was so emotionally exhausting, he did everything he could to rid himself of the Will Graham character after filming was completed. This included cutting his hair and dyeing it blonde, and shaving off his beard.
Played Missy Crider's father in the miniseries The Beast (1996). Crider later appeared in the second-season premiere of CSI: Crime Scene Investigation (2000).
Was 33 years old when Manhunter (1986) was released. When the film's remake, Red Dragon (2002), was released, his Will Graham successor, Edward Norton, was also 33 years old.
An avid Chicago Cubs fan, he sings "Take Me Out to the Ball Game" during the seventh-inning stretch at Wrigley Field every year and also narrated the documentary Wrigley Field: Beyond the Ivy (2001) about Wrigley Field.
Owns the rights of James Ellroy's crime novel "Clandestine".
Turned down a major part in Michael Mann's Heat (1995).
Has performed at the Steppenwolf Theater in Chicago.
Appears in The Skulls (2000) with Hill Harper. Harper currently co- stars in CSI: NY (2004), the spin-off of Petersen's series CSI: Crime Scene Investigation (2000).
Has been portrayed in several CSI games.
He has been an ensemble member of the Steppenwolf Theater Company in Chicago, Illinois, since 2008.
Shares his birthday with Larry Drake, who appeared with him in The Beast (1996).
He was nominated for a 1982 Joseph Jefferson Award for Actor in a Principal Role in a Play for "The Tooth of Crime" at the Remains Theatre in Chicago, Illinois.
He was awarded the 1984 Joseph Jefferson Award for Actor in a Principal Role in a Play for "In the Belly of the Beast" at the Wisdom Bridge Theatre in Chicago, Illinois.
He was nominated for a 1994 Joseph Jefferson Award for Actor in a Principal Role in a Play for "The Night of the Iguana" at the Goodman Theatre in Chicago, Illinois.
He was awarded the 2009 Joseph Jefferson Award for Actor in a Principal Role in a Play for "Blackbird" at the Victory Gardens Theater in Chicago, Illinois.
Has a second grandson named Indigo August, born in August 2009.
Longtime friend of Gary Cole.
Lived for a time with Amy Morton.
Has played the roles of both father and son, Joseph P. Kennedy and John F. Kennedy. Played Joseph P. Kennedy in The Kennedys of Massachusetts. Played John F. Kennedy in Rat Pack.
The actor who dubs his voice in Czech, Vladislav Benes, is also the Czech dubbing voice of Pierce Brosnan, Richard Gere, and Noah Wyle.
William's paternal grandfather, Jurgen Petersen, was born in Germany, to Danish parents, Andreas Christian Petersen and Anna Margaretha Ericksen. William's paternal grandmother, Lizzie Ricksher, was of German and French ancestry, while both of William's maternal grandparents, Arthur Cornelius Hoene and Katherine Vera Vollmar, were of German descent.
His name originates from the Germanic name Willahelm, which was composed of the elements wil "will, desire" and helm "helmet, protection".
Has two children: twins son and daughter (b. July 5, 2011).
Born on exactly the same date as Christine Ebersole (of "Richie Rich" fame).