Walt Whitman is often called the 'Father of Free Verse.' In 1855, he published the first edition of 'Leaves of Grass' at his own expense. It was a revolutionary book that broke all the rules of 19th-century poetry: it didn't use traditional rhyme or meter, and it celebrated the human body, democracy, and the common worker in explicit, sensual terms. Whitman spent the rest of his life revising and expanding the book, releasing nine different editions until his death in 1892. During the American Civil War, Whitman worked as a volunteer nurse in hospitals, an experience that led to his moving war poems like 'The Wound-Dresser' and his elegy for Abraham Lincoln, 'O Captain! My Captain!' His work sought to capture the vast, sprawling energy of the young United States and remains a cornerstone of American identity.