What is the full name of the author who wrote under the pen name 'Mark Twain'?

The full name of the author who wrote under the pen name “Mark Twain” is Samuel Langhorne Clemens.

Clemens was born in Florida, Missouri, in 1835 and grew up in Hannibal, a Mississippi River town that later inspired settings in The Adventures of Tom Sawyer and Adventures of Huckleberry Finn. Before becoming famous as a writer, he worked as a printer, typesetter, journalist, and steamboat pilot.

The name “Mark Twain” came from riverboat language. “Mark twain” meant that the water was two fathoms deep—about 12 feet—often considered a safe depth for navigation. Clemens began using the name professionally in the 1860s, and it eventually became more recognizable than his birth name.

A common mix-up is answering “Samuel Clemens.” That is an informal shortening, but the question asks for the full name, so “Samuel Langhorne Clemens” is the canonical answer. Twain became one of America’s best-known humorists and wrote major works including The Prince and the Pauper and Life on the Mississippi.