Walter Whitman Jr. (/ˈhwɪtmən/; 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."

Whitman was born on May 31, 1819, in West Hills, New York, the second of nine children of Quaker parents Walter and Louisa Van Velsor Whitman, of English and Dutch descent respectively. He was immediately nicknamed "Walt" to distinguish him from his father. At the age of four, Whitman moved with his family from Huntington to Brooklyn, living in a series of homes, in part due to bad investments. Whitman looked back on his childhood as generally restless and unhappy, given his family's difficult financial struggles. One happy moment that he later recalled was when he was lifted in the air and kissed on the cheek by the Marquis de Lafayette during a celebration of the setting of the Brooklyn Apprentices' Library's cornerstone by Lafayette in Brooklyn on July 4, 1825. Whitman later worked as a librarian at that institution.

At the age of 11, Whitman ended his formal schooling and sought employment to assist his family, which was struggling financially. He was an office boy for two lawyers and later was an apprentice and printer's devil for the weekly Long Island newspaper the Patriot, edited by Samuel E. Clements. There, Whitman learned about the printing press and typesetting. He may have written "sentimental bits" of filler material for occasional issues. Clements aroused controversy when he and two friends attempted to dig up the corpse of the Quaker minister Elias Hicks to create a plaster mold of his head. Clements left the Patriot shortly afterward, possibly as a result of the controversy.

The following summer Whitman worked for another printer, Erastus Worthington, in Brooklyn. His family moved back to West Hills, New York, on Long Island in the spring, but Whitman remained and took a job at the shop of Alden Spooner, editor of the leading Whig weekly newspaper the Long-Island Star. While at the Star, Whitman became a regular patron of the local library, joined a town debating society, began attending theater performances, and anonymously published some of his earliest poetry in the New-York Mirror. At the age of 16 in May 1835, Whitman left the Star and Brooklyn. He moved to New York City to work as a compositor though, in later years, Whitman could not remember where. He attempted to find further work but had difficulty, in part due to a severe fire in the printing and publishing district, and in part due to a general collapse in the economy leading up to the Panic of 1837. In May 1836, he rejoined his family, now living in Hempstead, Long Island. Whitman taught intermittently at various schools until the spring of 1838, though he was not satisfied as a teacher.

After his teaching attempts, Whitman returned to Huntington, New York, to found his own newspaper, the Long-Islander. Whitman served as publisher, editor, pressman, and distributor and even provided home delivery. After ten months, he sold the publication to E. O. Crowell, whose first issue appeared on July 12, 1839. There are no known surviving copies of the Long-Islander published under Whitman. By the summer of 1839, he found a job as a typesetter in Jamaica, Queens, with the Long Island Democrat, edited by James J. Brenton. He left shortly thereafter, and made another attempt at teaching from the winter of 1840 to the spring of 1841. One story, possibly apocryphal, tells of Whitman's being chased away from a teaching job in Southold, New York, in 1840. After a local preacher called him a "Sodomite", Whitman was allegedly tarred and feathered. Biographer Justin Kaplan notes that the story is likely untrue, because Whitman regularly vacationed in the town thereafter. Biographer Jerome Loving calls the incident a "myth". During this time, Whitman published a series of ten editorials, called "Sun-Down Papers—From the Desk of a Schoolmaster", in three newspapers between the winter of 1840 and July 1841. In these essays, he adopted a constructed persona, a technique he would employ throughout his career.