Mark Twain, born Samuel Langhorne Clemens, was a prolific American author and humorist. Twain is best known for his novels Adventures of Huckleberry Finn (1884), which has been called "the Great American Novel," and The Adventures of Tom Sawyer (1876). He is extensively quoted and is praised as the "greatest humorist the United States has produced," with William Faulkner calling him "the father of American literature."

Twain was raised in Hannibal, Missouri, which later provided the setting for both Tom Sawyer and Huckleberry Finn. He served an apprenticeship with a printer early in his career, and then worked as a typesetter, contributing articles to his older brother Orion Clemens' newspaper. Twain then became a riverboat pilot on the Mississippi River, which provided him the material for Life on the Mississippi (1883). Soon after, Twain headed west to join Orion in Nevada, humorously referring to his lack of success at mining and turning to journalism instead.

Twain first achieved success as a writer with the humorous story "The Celebrated Jumping Frog of Calaveras County," published in 1865, which brought him international attention. He wrote both fiction and non-fiction, and his wit and satire, both in prose and in speech, earned praise from critics and peers. Twain was a friend to presidents, artists, industrialists, and European royalty.

Although Twain initially supported American interests in the Hawaiian Islands, he later became vice president of the American Anti-Imperialist League from 1901 until his death in 1910, strongly opposing the Philippine–American War and American colonialism. Twain published a satirical pamphlet, "King Leopold's Soliloquy," in 1905 criticizing Belgian atrocities in the Congo Free State.

Twain earned a great deal of money from his writing and lectures but lost most of it in unsuccessful ventures like the Paige Compositor. He filed for bankruptcy, eventually overcoming his financial troubles with the help of Standard Oil executive Henry Huttleston Rogers, and paid all his creditors in full.

Twain was born shortly after the appearance of Halley's Comet and predicted that his death would accompany it. He died a day after the comet was closest to the Sun.