William Louis Petersen (born February 21, 1953) is an American actor and producer. He is best known for his role as Gil Grissom in the CBS drama series CSI: Crime Scene Investigation (2000–2015), for which he won a Screen Actors Guild Award and was nominated for a Golden Globe Award; he was further nominated for three Primetime Emmy Awards as a producer of the show. He reprised his role as Gil Grissom in the sequel CSI: Vegas, which premiered on October 6, 2021. He also starred in the films To Live and Die in L.A. (1985), Manhunter (1986), Young Guns II (1990), Fear (1996), The Contender (2000), Detachment (2011), and Seeking a Friend for the End of the World (2012). Early life Petersen was born in Evanston, Illinois, the youngest of six children of June (née Hoene; 1909–2006) and Arthur Edward Petersen (1907 – 2004), who worked in the furniture business. Of Danish and German descent, he 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. He was accepted to Idaho State University on a football scholarship. While at Idaho State, Petersen took an acting course, which changed the direction of his life. He left school along with his wife, Joanne, in 1974, and followed a drama professor to the Basque country, where he studied as a Shakespearean actor. Petersen was interested in Basque culture: He studied the Basque language and gave his daughter the Basque name "Maite Nerea" ("My Beloved"); she was born in Arrasate/Mondragón in 1975. Petersen returned to Idaho with the intention of being an actor. Not wanting to work a nonacting job in Idaho, he returned to the Chicago area, living with relatives. He became active in the theater and earned his Actors' Equity card. He performed with the Steppenwolf Theatre Company, of which he has been an ensemble member since 2008, and was a co-founder of the Remains Theater Ensemble, which also included other prominent Chicago actors Gary Cole and Ted Levine. Career In 1985, Petersen received his first break when he played a Secret Service agent gone rogue to avenge his mentor in William Friedkin's 1985 action film To Live and Die in L.A. In 1986, he played FBI agent Will Graham in the first