Poetry Foundation: William Butler Years PageWilliam Butler Yeats is widely considered to be one of the greatest poets of the 20th century. He belonged to the Protestant, Anglo-Irish minority that had controlled the economic, political, social, and cultural life of Ireland since at least the end of the 17th century. Most members of this minority considered themselves English people who happened to have been born in Ireland, but Yeats staunchly affirmed his Irish nationality.