Ross Macdonald was the main pseudonym used by the American-Canadian writer of crime fiction Kenneth Millar (/ˈmɪlər/; December 13, 1915 – July 11, 1983). He is best known for his series of hardboiled novels set in Southern California and featuring private detective Lew Archer. Since the 1970s, Macdonald's works (particularly the Archer novels) have received attention in academic circles for their psychological depth, sense of place, use of language, sophisticated imagery and integration of philosophy into genre fiction. Brought up in the province of Ontario, Canada, Macdonald eventually settled in the state of California, where he died in 1983.

The Wall Street Journal wrote that:

... it is the sheer beauty of Macdonald’s laconic style—with its seductive rhythms and elegant plainness—that holds us spellbound. "Hard-boiled," "noir," "mystery," it doesn’t matter what you call it. Macdonald, with insolent grace, blows past the barrier constructed by Dorothy Sayers between "the literature of escape" and "the literature of expression." These novels, triumphs of his literary alchemy, dare to be both.

Millar was born in Los Gatos, California, and raised in his Canadian parents' native Kitchener, Ontario. Millar was a Scots spelling of the surname Miller, and the author pronounced his name Miller rather than Millar. When his father abandoned the family unexpectedly when Millar was four years old, he and his mother lived with various relatives, and he had moved several times by his 16th year.

Back in Canada as a young adult, he graduated from the University of Western Ontario with an Honors degree in History and English. He found work as a high school teacher. Some years later, he attended the University of Michigan and received a PhD in 1952. He married Margaret Sturm in 1938, though they'd known each other earlier in high school. They had a daughter in 1939, Linda, who died in 1970. The family moved from Kitchener to Santa Barbara in 1946.

Millar began his career writing stories for pulp magazines and used his real name for his first four novels. Of these he completed the first, The Dark Tunnel, in 1944. After serving at sea as a naval communications officer from 1944 to 1946, Millar returned to Michigan, where he obtained his Ph.D. degree in literature. For his doctorate, Millar wrote a dissertation on Samuel Taylor Coleridge and studied under poet W. H. Auden. Unusual for a prominent literary intellectual of the era, Auden held mystery or detective fiction could rise to the level of literature and encouraged Millar's interest in the genre.

For his fifth novel, in 1949, he wrote under the name John Macdonald (his father's first and middle names) in order to avoid confusion with his wife, who was achieving her own success writing as Margaret Millar. He then changed his pen name briefly to John Ross Macdonald, before settling on Ross Macdonald (Ross borrowed from a favorite cousin) in order to avoid being confused with fellow mystery writer John D. MacDonald, who was writing under his real name. Millar would use the pseudonym Ross Macdonald on all his fiction from the mid '50s forward.

Most of his books were set primarily in and around his adopted hometown of Santa Barbara. In these works, the city where Lew Archer is based goes under the fictional name of Santa Teresa.