Patrick O'Brian (12 December 1914 – 2 January 2000), born Richard Patrick Russ, was an English novelist and translator, best known for his Aubrey–Maturin series of sea novels set in the Royal Navy during the Napoleonic Wars, and centered on the friendship of the English naval captain Jack Aubrey and the Irish–Catalan physician Stephen Maturin. The 20-novel series, the first of which is Master and Commander, is known for its well-researched and highly detailed portrayal of early 19th-century life, as well as its authentic and evocative language. A partially finished 21st novel in the series was published posthumously containing facing pages of handwriting and typescript.

O'Brian wrote a number of other novels and short stories, most of which were published before he achieved success with the Aubrey–Maturin series. He also translated works from French to English, and wrote biographies of Joseph Banks and Picasso. His major success as a writer came late in life, when the Aubrey–Maturin series caught the eye of an American publisher. The series drew more readers and favourable reviews when the author was in his seventies. Near the end of his life, and in the same year that he lost his wife, British media revealed details of O'Brian's early life, first marriage, and post-war change of name, causing distress to the very private author and to many of his readers at that time.

Patrick O'Brian's acclaimed Aubrey-Maturin series of historical novels has been described as "a masterpiece" (David Mamet, New York Times), "addictively readable" (Patrick T. Reardon, Chicago Tribune), and "the best historical novels ever written" (Richard Snow, New York Times Book Review), which "should have been on those lists of the greatest novels of the 20th century" (George Will). The series centers on the enduring friendship between naval officer Jack Aubrey and physician (and spy) Stephen Maturin. The Far Side of the World, the tenth book in the series, was adapted into a 2003 film directed by Peter Weir and starring Russell Crowe and Paul Bettany. The film was nominated for several awards.