William Butler Yeats (1865-1939) was an Irish poet, playwright, and political activist who was one of the most important figures of the Irish literary revival. He is known for his use of Irish mythology and for his exploration of the themes of love, death, and rebirth. His most famous works include "The Tower" and "The Wild Swans at Coole." Yeats was also a senator in the Irish Free State and was awarded the Nobel Prize in Literature in 1923.