Eugene Gladstone O'Neill (October 16, 1888 – November 27, 1953) was an American playwright and Nobel laureate in literature. O'Neill was born in a Broadway hotel room in Longacre Square (now Times Square), in the Barrett Hotel, to an Irish immigrant father and a mother of Irish descent. His father was an actor and his mother accompanied him on frequent tours with a theater company, so Eugene was sent to a Catholic boarding school, where he discovered a love of reading. He decided to devote himself full-time to writing plays after his experience in 1912–13 at a sanatorium where he was recovering from tuberculosis. O'Neill had previously written poetry and been employed by the New London Telegraph, as a reporter.

In the 1910's, O'Neill became a part of the Greenwich Village literary scene, including the Provincetown Players, which staged his early plays. His work was influenced by "radical" thinkers like Communist Labor Party founder John Reed. O'Neill brought to American drama techniques of realism earlier associated with Russian playwright Anton Chekhov, Norwegian playwright Henrik Ibsen, and Swedish playwright August Strindberg. His plays were among the first to include speeches in American vernacular and involve characters on the fringes of society, where they struggle to maintain their hopes and aspirations, but ultimately slide into disillusionment and despair.

O'Neill's first published play, Beyond the Horizon, opened on Broadway in 1920 to great acclaim, and was awarded the Pulitzer Prize for Drama. His first major hit was The Emperor Jones, which also ran on Broadway in 1920, and obliquely commented on the U.S. occupation of Haiti that was a topic of debate in that year's presidential election.  His best-known plays include Anna Christie (Pulitzer Prize 1922), Desire Under the Elms (1924), Strange Interlude (Pulitzer Prize 1928), Mourning Becomes Electra (1931), and his only well-known comedy, Ah, Wilderness!, a wistful re-imagining of his youth. In 1936, he received the Nobel Prize for Literature. After a ten-year hiatus, O'Neill's now-renowned play The Iceman Cometh was produced in 1946. The following year, A Moon for the Misbegotten failed to make an impression, but decades later gained recognition as being among his best works.

O'Neill suffered from many illnesses in his life, including alcoholism and depression, and Parkinsons-like tremors took away his ability to write the last 10 years of his life, leaving many scripts unfinished. He died (also in a hotel room) in Boston, Mass., in 1953. Both Iceman and Moon were heavily autobiographical in nature, as was Long Day's Journey Into Night, widely considered to be his finest, but published and produced posthumously. Although his written instructions had stipulated that it not be made public until 25 years after his death, it was published in 1956 and produced on stage to tremendous critical acclaim and won the Pulitzer Prize in 1957. Other posthumously-published works include A Touch of the Poet (1958) and More Stately Mansions (1967).