David Duchovny as Fox Mulder
Fun Fact: Although his character in the show is a hardcore believer in the paranormal and extraterrestrial life, Duchovny is actually a skeptic in real life. At the same time, Gillian Anderson, whose character is a skeptic in the show, is actually a believer in real life.
Gillian Anderson as Dana Scully
Fun Fact: Gillian Anderson was only 24 years old when she was cast in the show.
Mitch Pileggi as Walter Skinner
Fun Fact: Pileggi worked as a defense contractor in Iran before moving back to the U.S. in 1978 in the midst of the Iranian Revolution.
Nicholas Lea as Alex Krycek
Fun Fact: The character of Alex Krycek was originally meant to replace Dana Scully for only three episodes, while Anderson was away on maternity leave. The character ended up lasting eight seasons.
Robert Patrick as John Doggett
Fun Fact: TV Guide named Robert Patrick’s Agent John Doggett as one of the “10 Sexiest Men in Sci-Fi.”
Annabeth Gish as Monica Reyes
Fun Fact: Annabeth Gish is related to silent film actors Dorothy and Lillian Gish, the latter of whom appeared in the 1915 D.W. Griffith controversial classic Birth of a Nation.
William B. Davis as Cigarette Smoking Man
Fun Fact: According to producer Kim Manners, at the start of the show, Davis was only supposed to be an extra leaning against a shelf. He would go on to play the main antagonist of the show.
Jerry Hardin as "Deep Throat"
Fun Fact: The role of "Deep Throat" was originally supposed to appear one time in the first season. However, he became a recurring character throughout the first season, appearing sporadically throughout the series.
Steven Williams as Mr. X
Fun Fact: Entertainment Weekly listed Mr. X at No. 17 in their list of "20 Black Sci-Fi Icons."
Laurie Holden as Marita Covarrubias
Fun Fact: Laurie Holden was 25 years old when she was cast in the role.
Brian Thompson as the Alien Bounty Hunter
Fun Fact: Thompson was cast in The Terminator, along with Bill Paxton, while he was still in high school.
Jeff Gulka as Gibson Andrew Praise
Fun Fact: Today, Jeff Gulka plays organs and piano for his band The Wicks.
Dean Haglund, Tom Braidwood, and Bruce Harwood as The Lone Gunmen (Langly, Frohike, Byers)
Interesting Fact: In the pilot episode of their spin-off series, the Gunmen try to stop a hijacked plane from crashing into the World Trade Center. The episode aired six months before September 11, 2001.