Billy Wilder (; German: [ˈvɪldɐ]; born Samuel Wilder; June 22, 1906 – March 27, 2002) was an Austrian-American filmmaker. His career in Hollywood spanned five decades, and he is regarded as one of the most brilliant and versatile filmmakers of Classic Hollywood cinema. He was nominated for the Academy Award for Best Director eight times, winning twice, and for a screenplay Academy Award 13 times, winning three times.

Wilder became a screenwriter while living in Berlin. The rise of the Nazi Party and antisemitism in Germany saw him move to Paris. He then moved to Hollywood in 1933, and had a major hit when he, Charles Brackett and Walter Reisch wrote the screenplay for the Academy Award-nominated film Ninotchka (1939). Wilder established his directorial reputation and received his first nomination for the Academy Award for Best Director with the film noir Double Indemnity (1944), based on the novel by James M Cain with a screenplay by Wilder and Raymond Chandler. Wilder won the Best Director and Best Screenplay Academy Awards for the film adaptation of the novel The Lost Weekend (1945), which also won the Academy Award for Best Picture.

In the 1950s, Wilder directed and co-wrote a string of critically acclaimed films, including the Hollywood drama Sunset Boulevard (1950), for which he won his second screenplay Academy Award; Ace in the Hole (1951), Stalag 17 (1953) and Sabrina (1954). Wilder directed and co-wrote three films in 1957, including The Spirit of St. Louis, Love in the Afternoon and Witness for the Prosecution. Wilder directed Marilyn Monroe in two films, The Seven Year Itch (1955) and Some Like It Hot (1959). In 1960, Wilder co-wrote, directed and produced the critically acclaimed film The Apartment. It won Wilder Academy Awards for Best Picture, Best Director and Best Original Screenplay. Beginning with Some Like It Hot and The Apartment, he made seven films with Jack Lemmon, four of which co-starred Walter Matthau; the threesome's first collaboration was The Fortune Cookie (1966). Other notable films Wilder directed include One, Two, Three (1961), Irma la Douce (1963), Kiss Me, Stupid (1964) and Avanti! (1972). Wilder directed fourteen actors in Oscar-nominated performances.

Wilder received various honors over his distinguished career between the late 1980s and 1990s. He received the British Academy Film Award Fellowship Award, the Directors Guild of America's Lifetime Achievement Award, the Laurel Award for Screenwriting Achievement, and the Producers Guild of America's Lifetime Achievement Award. Double Indemnity, Sunset Boulevard, Some Like It Hot, and The Apartment are included in the AFI's greatest American films of all time. As of 2019, seven of his films are preserved in the United States National Film Registry of the Library of Congress as being "culturally, historically or aesthetically significant". Anthony Lane writes that Double Indemnity, The Seven Year Itch, Sunset Boulevard and The Apartment are "part of the lexicon of moviegoing" and that Some Like It Hot is a "national treasure." Roger Ebert asked, "Of all the great directors of Hollywood's golden age, has anybody made more films that are as fresh and entertaining to this day as Billy Wilder's?...And who else can field three contenders among the greatest closing lines of all time?", citing the closing lines of Sunset Boulevard, Some Like it Hot, and The Apartment. Wilder's epitaph, a paraphrase of the last line of Some Like It Hot, is "I'm a writer but then nobody's perfect."