Grissom is a forensic entomologist and for the series' first nine seasons, a CSI Level III Supervisor employed by the Las Vegas Police Department.

Anthony E. Zuiker, who created the show, loosely based Grissom on real life Las Vegas Metropolitan Police Department criminalist Daniel Holstein.

When Petersen's nephew died, he flew home and was unavailable for the filming of the episode, which was rewritten to be centered on Nick.

[9] During 2007 (CSI's season seven), William Petersen took a break from CSI to appear in a five-week run of the Trinity Repertory Company production of Dublin Carol in Providence, Rhode Island, resulting in Grissom taking a sabbatical, being replaced by Liev Schreiber, as Michael Keppler, who developed a small story arc through "Sweet Jane", "Redrum", and "Meet Market".

Grissom's father taught botany at a local college and passed his enthusiasm for natural sciences onto his son.

Consequently, as a young child, Grissom "played doctor" by performing necropsies on small, deceased animals in the local area.

In the episode "Grissom vs. the Volcano", Catherine tells the story of losing at a science competition as a child against a "kid with some lame red ants."

[12] At the same time, he also attended boxing matches to learn about the patterns of bruise formations on bodies and eventual blood spatters from the injuries.

Grissom once mentioned losing a body while in Minneapolis, implying he spent time there before taking a job in Las Vegas.

[14] He became the night shift team supervisor for the Las Vegas CSI unit on the second episode of the series, after Jim Brass was demoted following the death of co-worker Holly Gribbs.

Rather than leave in the middle of a case, Grissom stayed on to help solve it, and ultimately proved instrumental in saving the life of a woman who would have been the killer's latest victim.

The case closed, Grissom, having already had a series of one-on-one farewells with his co-workers, silently left the crime lab and departed for Costa Rica for a reunion with fiancée Sara Sidle, an allusion perhaps to his comments in a season one episode that when he left, people would not throw a party for him because he was not the sort of person whom people would get deeply involved with.

After reuniting with Sara Sidle, Grissom presumably remains in Costa Rica for a short time, before guest-lecturing at the Sorbonne, as noted in the tenth season.

After his activities lead him to the Port of San Diego, Grissom reunites with Willows and the CSI team in order to consult on a series of bombings in Las Vegas.

[22] In the season two episode "Alter Boys", Grissom confides in a priest that he does not believe in the concept of organized religion and is a lapsed Catholic but does believe in the idea of God.

In "Two and a Half Deaths", Jim Brass was talking about a TV program that he thought had already "jumped the shark," but Grissom did not know the term.

At the beginning of the show, he was referred to as "Gruesome Grissom" for his sometimes morbid fascination with the more bizarre aspects of man and nature.

[32] In "The Grave Shift", even after his office has been cleared out (and later reclaimed by a somewhat-reluctant Nick Stokes after Catherine Willows passed on the offer), the fetal pig in a jar was placed back in there by Hodges, who stated simply that "[it] belongs here."

Like Holmes, Grissom is dispassionate with a fierce devotion to logic and little regard for societal norms of behavior; Grissom once smashed mustard jars in a grocery store to illustrate a theory ("I-15 Murders"), much as Holmes once practiced spearing a pig in a butcher's to determine how strong a man would have to be to transfix a man with a harpoon.

Grissom possesses a Moriarty-like nemesis, Paul Millander, whom he pursues in several episodes ("Pilot", "Anonymous", and "Identity Crisis").

In the sixth-season episode "Bang-Bang", Grissom tells Doc Robbins, concerning a woman shot in the mouth, "This was someone who was emotionally close to her."

Grissom may not ask to take on the role of mentor, but it seems to happen naturally, going all the way back to Sara Sidle when they first met in San Francisco, then Nick Stokes and Greg Sanders in Vegas.

He also shares a good friendship with Dr. Al Robbins and the two were seen singing together in the autopsy room while processing the body of a murdered rock 'n' roll star (season 7, "Built to Kill, Part 2").

Some fans have always expected to see a relationship between Grissom and Catherine Willows, in whom he is shown confiding many times, once even likening her to being his "wife.

[46][47] By killing off the sexual tension between the two characters and making them an item, the production crew were seen to be adding more personal drama to the show, increasing the appeal to some of Grey's Anatomy's younger audience.

Once they see each other, they embrace in a passionate kiss, and Sara's return to CSI in the first episode of season ten reveals that she and Grissom are now married.

[59] There are also many other sites that update daily news about either Gil Grissom's status on CSI or William Petersen's activities in real life.

The auction ended on October 7 with the prop being sold for US$15,600, which CBS donated to the National Center on Addiction and Substance Abuse Association.

[62] CSI: Crime Scene Investigation executive producer and showrunner Carol Mendelsohn considers Grissom the center of the show.

[63] Grissom has received positive responses from critics, ranking number 82 on Bravo's 100 Greatest TV Characters list, along with Catherine Willows.