Walt Whitman is the influential poet recognized for his profound explorations of nature and humanity. His seminal work, Leaves of Grass, published in 1855, broke conventional poetic forms and celebrated individuality and the human spirit. Whitman's free verse style and celebration of the interconnectedness of life have left a lasting impact on American literature. His themes of democracy, equality, and the human experience resonate powerfully, making him a pivotal figure in the Transcendentalist movement.