The renowned poet and author known for their collection "Leaves of Grass" is Walt Whitman. First published in 1855, this groundbreaking work celebrates the beauty of nature, the human spirit, and the diversity of American life. Whitman's free verse style and embracing of unconventional themes marked a shift in poetry, reflecting the complexities of democracy and individuality. His optimistic and inclusive vision contributed significantly to the American literary canon and the subsequent development of modern poetry.