Samuel Langhorne Clemens (November 30, 1835 – April 21, 1910), best known by his pen name Mark Twain, was an American writer, humorist, entrepreneur, publisher, and lecturer. He was praised as the "greatest humorist the United States has produced", and William Faulkner called him "the father of American literature". His novels include The Adventures of Tom Sawyer (1876) and its sequel, Adventures of Huckleberry Finn (1884), the latter of which has often been called the "Great American Novel". Twain also wrote A Connecticut Yankee in King Arthur's Court (1889) and Pudd'nhead Wilson (1894), and co-wrote The Gilded Age: A Tale of Today (1873) with Charles Dudley Warner.

Twain was raised in Hannibal, Missouri, which later provided the setting for Tom Sawyer and Huckleberry Finn. He served an apprenticeship with a printer and then worked as a typesetter, contributing articles to the newspaper of his older brother Orion Clemens. He later became a riverboat pilot on the Mississippi River before heading west to join Orion in Nevada. He referred humorously to his lack of success at mining, turning to journalism for the Virginia City Territorial Enterprise. His humorous story "The Celebrated Jumping Frog of Calaveras County" was published in 1865, based on a story that he heard at Angels Hotel in Angels Camp, California, where he had spent some time as a miner. The short story brought international attention and was even translated into French. His wit and satire, in prose and in speech, earned praise from critics and peers, and he was a friend to presidents, artists, industrialists, and European royalty. Although initially an ardent American imperialist who spoke out strongly in favor of American interests in the Hawaiian Islands, he later became vice president of the American Anti-Imperialist League from 1901 until his death in 1910, coming out strongly against the Philippine-American War.

Twain earned a great deal of money from his writing and lectures, but invested in ventures that lost most of it, such as the Paige Compositor, a mechanical typesetter that failed because of its complexity and imprecision. He filed for bankruptcy in the wake of these financial setbacks, but in time overcame his financial troubles with the help of Standard Oil executive Henry Huttleston Rogers. He eventually paid all his creditors in full, even though his declaration of bankruptcy meant he was not required to do so.

Twain was born shortly after an appearance of Halley's Comet, and he predicted that he would "go out with it" as well, dying a day after the comet was at its closest to Earth.