Walt Whitman was an American poet, essayist, and journalist, celebrated as one of the most influential poets in American literature. Known as the father of free verse, his work combined transcendentalism and realism. His 1855 collection Leaves of Grass was both groundbreaking and controversial for its sensuality. Whitman worked in hospitals during the Civil War, and his poetry often reflected themes of loss and healing. His influence on poetry endures, with many regarding him as a quintessential voice of American culture.