Stephen Joshua Sondheim (born March 22, 1930) is an American composer and lyricist for stage and film. He is the winner of an Academy Award, multiple Tony Awards (nine, more than any other composer) including the Special Tony Award for Lifetime Achievement in the Theatre (received 2008), multiple Grammy Awards, and a Pulitzer Prize. He has been described as "the greatest and perhaps best-known artist in the American musical theatre." His most famous scores include (as composer/lyricist) A Funny Thing Happened on the Way to the Forum, Company, Follies, A Little Night Music, Sweeney Todd, Sunday in the Park with George, Into the Woods, and Assassins, as well as the lyrics for West Side Story and Gypsy. He was president of the Dramatists Guild from 1973 to 1981.

Stephen Sondheim was born to Herbert and Janet ("Foxy") Sondheim, in New York City, and grew up on the Upper West Side of Manhattan and later on a farm in Pennsylvania, after his parents divorced. While living in New York, Stephen Sondheim attended the Ethical Culture Fieldston School. Herbert, his father, was a dress manufacturer and Foxy, his mother, designed the dresses. An only child of well-to-do parents living in a high-rise apartment on Central Park West, Sondheim's childhood has been portrayed as isolated and emotionally neglected in Meryle Secrest's biography, Stephen Sondheim: A Life. He graduated New York Military Academy in 1946.

Sondheim traces his interest in theater to Very Warm for May, a Broadway musical he saw at the age of nine. "The curtain went up and revealed a piano," Sondheim recalled. "A butler took a duster and brushed it up, tinkling the keys. I thought that was thrilling."