William Butler Yeats spent his life building a mythology, and then watching the real world burn through it. He began as a dreamer of the Celtic twilight -- faeries, ancient heroes, misty lakes -- and ended as the fiercest, most clear-eyed poet of the twentieth century, a man who could look at the wreckage of civilization and describe it in language that sounded like hammered bronze.

He was born in Dublin in 1865, the eldest son of the painter John Butler Yeats. His childhood was divided between London and Sligo, the wild western county that became his imaginative homeland. He was a poor student, dreamy and half-blind without the glasses he often refused to wear. What he lacked in conventional learning he replaced with obsession: Irish mythology, the occult, the poetry of Shelley and Blake, and the theater.

And then there was Maud Gonne. She was tall, beautiful, fiercely political, and absolutely unattainable. Yeats proposed to her at least four times over three decades. She refused him every time. She married a man Yeats despised, John MacBride, who was later executed for his role in the Easter Rising of 1916. Yeats's unrequited love for Gonne is one of the great engines of English poetry -- it drove him from the languorous beauty of his early verse into the hard, passionate clarity of his mature work.

"Easter 1916" marks the turn. The poem about the failed republican uprising -- the execution of its leaders, including MacBride -- contains the phrase that would haunt Irish history: "A terrible beauty is born." In six words, Yeats captured the paradox of political violence: that sacrifice creates a beauty inseparable from destruction, and that naming it is both an act of commemoration and of warning.

The poems that followed -- "The Second Coming," "Sailing to Byzantium," "Among School Children," the towering sequences of The Tower and The Winding Stair -- are among the greatest achievements of modernist literature. "The Second Coming," written in 1919 amid the wreckage of World War I and the Irish War of Independence, prophesied the century's horrors with terrifying precision: "Things fall apart; the centre cannot hold; / Mere anarchy is loosed upon the world."

Yeats won the Nobel Prize in 1923. He served as a senator in the new Irish Free State. He explored mysticism, automatic writing, and a private symbolic system mapped in his strange book A Vision. He married Georgie Hyde-Lees, who proved both patient and genuinely psychic, and fathered two children.

He died in France in January 1939, months before the war he had, in a sense, predicted. His body was returned to Sligo in 1948, to the churchyard at Drumcliff, beneath Ben Bulben. His epitaph, written by himself, is characteristically imperious: "Cast a cold eye / On life, on death. / Horseman, pass by!" Even his gravestone is a poem.