After an impressive nine-year run as the star of "CSI," William Petersen is leaving the small screen behind and returning to the stage.

Because of the rampant success of "CSI," Petersen has decided to leave the show because he was concerned about becoming too comfortable in his career.

Since its debut in 2000, "CSI" has become one of the most popular shows in the world, spawning two spin-off series and countless imitators. At the centre of it all was Petersen's Golden Globe nominated performance as the iconic Gil Grissom, with a wry one-liner and a fascination with insects.

Since the taping of his last episode, Petersen has traded in millions of viewers, for small, intimate audiences of 300 as he returned to his roots as a theatre actor in Chicago.

But fans shouldn't fret; Petersen's on-stage roles won't keep him completely away from "CSI," as the actor plans on remaining a producer on the show and will occasionally make guest appearances in the future.

Gil Grissom's long goodbye

Grissom's departure has been a long time coming on "CSI." Last season, fiancée and fellow investigator Sara (Jorja Fox) fled Las Vegas, and in this season's premiere, the unexpected shooting death of Warrick (Gary Dourdan) sent Grissom into an emotional tailspin and expedited his withdrawal from the Las Vegas Crime Lab.

In his final episode, airing Thursday, January 15 on CTV, Grissom takes on his final case, and will invite Professor Langston (Laurence Fishburne), to join his team as a level one CSI.

Oscar nominee Fishburne hasn't appeared in a TV series since "Pee-wee's Playhouse" in the mid-'80s, but is best known as his role as Morpheus in "The Matrix" trilogy.

Speaking to reporters last year, Fishburne said he hadn't even seen one episode of the series before being offered the role, but after watching the show admits he was drawn to its dark and moody quality.

Fishburne's character, Professor Langston, first appeared on the show in an episode which aired on December 11 as a college lecturer and former pathologist. The dark twist? Like the subjects he studies, he also possesses a chromosome found in serial killers.

It was his college seminar on serial killers, featuring the notorious murderer Nate Haskell on a two-way camera that caught Grissom's attention.

Grissom was attending Langston's lectures undercover, in order to investigate a rash of murders that followed the patterns of Haskell's previous killing sprees. Langston was initially resentful of Grissom's undercover approach, but they eventually joined forces to capture Haskell's accomplice.

As Grissom bids farewell, Langston's transitions into the CSI team will be fraught with challenges. From bungling his first crime scene to struggling with the late-night hours, Langston has his work cut out for him.