William Butler Yeats (/ˈjeɪts/; 13 June 1865 – 28 January 1939) was an Irish poet and one of the foremost figures of 20th century literature. A pillar of both the Irish and British literary establishments, in his later years he served as an Irish Senator for two terms. Yeats was a driving force behind the Irish Literary Revival and, along with Lady Gregory, Edward Martyn, and others, founded the Abbey Theatre, where he served as its chief during its early years. He largely renounced the transcendental beliefs of his youth, though he remained preoccupied with physical and spiritual masks, as well as with cyclical theories of life.