Walter Whitman Jr. (; May 31, 1819 – March 26, 1892) was an American poet, essayist and journalist. A humanist, he was a part of the transition between transcendentalism and realism, incorporating both views in his works. Whitman is among the most influential poets in the American canon, often called the father of free verse. His work was controversial in his time, particularly his 1855 poetry collection Leaves of Grass, which was described as obscene for its overt sensuality.

Born in Huntington on Long Island, Whitman resided in Brooklyn as a child and through much of his career. At the age of 11, he left formal schooling to go to work. Later, Whitman worked as a journalist, a teacher, and a government clerk. Whitman's major poetry collection, Leaves of Grass, was first published in 1855 with his own money and became well known. The work was an attempt at reaching out to the common person with an American epic. He continued expanding and revising it until his death in 1892. During the American Civil War, he went to Washington, D.C. and worked in hospitals caring for the wounded. His poetry often focused on both loss and healing. On the death of Abraham Lincoln, whom Whitman greatly admired, he wrote his well known poems, "O Captain! My Captain!" and "When Lilacs Last in the Dooryard Bloom'd", and gave a series of lectures. After a stroke towards the end of his life, Whitman moved to Camden, New Jersey, where his health further declined. When he died at the age of 72, his funeral was a public event.

Whitman's influence on poetry remains strong. Mary Whitall Smith Costelloe argued: "You cannot really understand America without Walt Whitman, without Leaves of Grass ... He has expressed that civilization, 'up to date,' as he would say, and no student of the philosophy of history can do without him." Modernist poet Ezra Pound called Whitman "America's poet ... He is America."