William Petersen

William Louis Petersen was born on February 21, 1953, in Evanston, Illinois, the youngest of six children born to June (née Hoene) and Arthur Edward Petersen, who worked in the furniture business. Of Danish and German descent, Petersen was raised in the Roman Catholic faith of his mother. He has two brothers, Arthur Jr. and Robert, and three sisters, Anne, Mary Kay, and Elizabeth. He graduated from Bishop Kelly High School in Boise, Idaho, in 1972 and was accepted to Idaho State University on a football scholarship. While enrolled there, he took an acting course that redirected his ambitions. In 1974, he and his wife Joanne left college and traveled with a drama professor to the Basque country, where Petersen studied as a Shakespearean actor. He also immersed himself in Basque culture, learning the Basque language and giving his daughter, born in Arrasate/Mondragón in 1975, the Basque name Maite Nerea.

Returning to the Chicago area, Petersen became active in the local theater community and earned his Actors' Equity card. He performed with the Steppenwolf Theatre Company, of which he has been an ensemble member since 2008, and co-founded the Remains Theater Ensemble alongside actors Gary Cole and Ted Levine. His Broadway career includes a 1996 appearance in The Night of the Iguana.

Petersen made his film debut with a small part in Michael Mann's Thief in 1981. His first significant film role came in William Friedkin's To Live and Die in L.A. (1985), in which he played a Secret Service agent seeking to avenge his mentor. The following year he portrayed FBI agent Will Graham in Manhunter (1986), the first film to feature the character of Hannibal Lecter. He declined a role in Oliver Stone's Platoon to remain closer to his family, and instead appeared in the 1987 HBO film Long Gone as minor league baseball player and manager Cecil "Stud" Cantrell. In 1990, he played Ambassador Joseph P. Kennedy in the ABC miniseries The Kennedys of Massachusetts and portrayed Pat Garrett in Young Guns II. He played a father determined to end his daughter's dangerous relationship in Fear (1996) and appeared as Governor Jack Hathaway in The Contender (2000). Additional film credits include Young Guns II (1990), Kiss the Sky (1999), the 1997 television remake of 12 Angry Men as Juror #12, Detachment (2011), and Seeking a Friend for the End of the World (2012).

From 2000 to 2009, Petersen starred as Dr. Gil Grissom in the CBS crime drama CSI: Crime Scene Investigation, a role for which he won a Screen Actors Guild Award, received a Golden Globe Award nomination, and earned three Primetime Emmy Award nominations as a producer of the series. He renewed his contract with CBS for the 2008–09 season at a reported $600,000 per episode before departing as a series regular following Season 9's tenth episode to pursue stage work, while continuing as an executive producer. He reprised the role of Grissom in the Season 11 episode "The Two Mrs. Grissoms," which aired on February 3, 2011, and returned again for the series finale, "Immortality," in 2015. In 2021, he reprised the character once more in the sequel series CSI: Vegas, which premiered on October 6, 2021. In October 2025, Petersen stated he was retired from acting and was not seeking new roles.

During his run on CSI, Petersen took a break in 2006 to appear in a five-week production of Dublin Carol by Conor McPherson at the Trinity Repertory Company in Providence, Rhode Island. On February 3, 2009, he received a star on the Hollywood Walk of Fame.

In his personal life, Petersen and his first wife, Joanne Brady, had a daughter, Maite, in 1975 and later divorced. In June 2003, he married Gina Cirone, and on July 5, 2011, the couple welcomed twins, a daughter and a son, via surrogate. In August 2021, Petersen was taken to a hospital by ambulance after experiencing symptoms of exhaustion following twelve weeks of shooting CSI: Vegas and was released shortly thereafter.