Christopher Haden-Guest, 5th Baron Haden-Guest (born February 5, 1948), known professionally as Christopher Guest, is an American and British actor, comedian, screenwriter and director. Guest has written, directed, and starred in his series of comedy films shot in mockumentary style. He co-wrote and acted in the rock satire This Is Spinal Tap (1984), and later directed a string of satirical mockumentary films such as Waiting for Guffman (1996), Best in Show (2000), A Mighty Wind (2003), For Your Consideration (2006), and Mascots (2016). He also acted in the films Death Wish (1974), Little Shop of Horrors (1986), The Princess Bride (1987), and A Few Good Men (1992); and was a regular cast member on the 10th season of Saturday Night Live.

Guest holds a hereditary British peerage as the 5th Baron Haden-Guest. He was active in the House of Lords until the 1999 reform abolished his seat. When using his title, he is normally styled as Lord Haden-Guest. Guest is married to the actress Jamie Lee Curtis.

Guest was born on February 5, 1948 in New York City, the son of Peter Haden-Guest, a British United Nations diplomat who later became the 4th Baron Haden-Guest, and his second wife, the former Jean Pauline Hindes, an American former vice president of casting at CBS. Guest's paternal grandfather, Leslie, Baron Haden-Guest, was a Labour Party politician, who was a convert to Judaism. Guest's paternal grandmother, a descendant of the Dutch Jewish Goldsmid family, was the daughter of Colonel Albert Goldsmid who founded the Jewish Lads Brigade and the Maccabaeans. Guest's maternal grandparents were Jewish emigrants from Russia. Both of Guest's parents had become atheists, and Guest himself had no religious upbringing. In 1938, his uncle, David Guest, a lecturer and Communist Party member, was killed in the Spanish Civil War, fighting in the International Brigades.

Guest spent parts of his childhood in his father's native United Kingdom. He attended the High School of Music & Art (New York City), studying classical music (clarinet) at the Stockbridge School in the village of Interlaken in Stockbridge, Massachusetts. He later took up the mandolin, became interested in country music, and played guitar with Arlo Guthrie, a fellow student at Stockbridge School. Guest later began performing with bluegrass bands until he took up rock and roll. Guest went to Bard College for a year and then studied acting at New York University's Graduate Acting Program at the Tisch School of the Arts, graduating in 1971.

Guest began his career in theatre during the early 1970s with one of his earliest professional performances being the role of Norman in Michael Weller's Moonchildren for the play's American premiere at the Arena Stage in Washington, DC, in November 1971. Guest continued with the production when it moved to Broadway in 1972. The following year, he began making contributions to The National Lampoon Radio Hour for a variety of National Lampoon audio recordings. He both performed comic characters (Flash Bazbo—Space Explorer, Mr. Rogers, music critic Roger de Swans, and sleazy record company rep Ron Fields) and wrote, arranged, and performed numerous musical parodies (of Bob Dylan, James Taylor, and others). He was featured alongside Chevy Chase and John Belushi in the off-Broadway revue National Lampoon's Lemmings. Two of his earliest film roles were small parts as uniformed police officers in the 1972 film The Hot Rock and 1974's Death Wish.

Along with Bill Murray, Brian Doyle-Murray, and others, Guest was one of the "Prime Time Players" on Saturday Night Live with Howard Cosell. This was the short-lived variety show that aired from September 20, 1975, to January 17, 1976, not to be confused with the long-running sketch show Saturday Night Live, which began airing a month later and lampooned the group by billing their own sketch comedy actors as "The Not Ready for Prime Time Players".

Guest played a small role in the 1977 All in the Family episode "Mike and Gloria Meet", where in a flashback sequence Mike and Gloria recall their first blind date, set up by Michael's college buddy Jim (Guest), who dated Gloria's girlfriend Debbie (Priscilla Lopez).

Guest also had a small but important role in It Happened One Christmas, the 1977 gender-reversed TV remake of the Frank Capra classic It's a Wonderful Life, starring Marlo Thomas as Mary Bailey (the Jimmy Stewart role), with Cloris Leachman as Mary's guardian angel and Orson Welles as the villainous Mr. Potter. Guest played Mary's brother Harry, who returned from the Army in the final scene, speaking one of the last lines of the film: "A toast! To my big sister Mary, the richest person in town!"