Walter Whitman Jr. (; May 31, 1819 – March 26, 1892) was an American poet, essayist, and journalist; he also wrote two novels. He is considered one of the most influential poets in American literature and world literature. Whitman incorporated both transcendentalism and realism in his writings and is 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 by some as obscene for its overt sensuality.

Whitman was born in Huntington on Long Island and lived in Brooklyn as a child and through much of his career. At age 11, he left formal schooling to go to work. He worked as a journalist, a teacher, and a government clerk. Whitman's major poetry collection, Leaves of Grass, first published in 1855, was financed with his own money and became well known. The work was an attempt to reach out to the common person with an American epic. Whitman continued expanding and revising Leaves of Grass 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 assassination of Abraham Lincoln, whom Whitman greatly admired, he authored a number of poems, including "O Captain! My Captain!" and "When Lilacs Last in the Dooryard Bloom'd", and gave a series of lectures on Lincoln. After suffering a stroke towards the end of his life, Whitman moved to Camden, New Jersey, where his health further declined. When he died at age 72, his funeral was a public event.

Whitman's influence on poetry remains strong. Art historian Mary Berenson wrote, "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." According to the Poetry Foundation, he is "America's world poet—a latter-day successor to Homer, Virgil, Dante, and Shakespeare."