Mark Twain, whose real name was Samuel Langhorne Clemens, was a famous American humorist, novelist, writer, and lecturer. He gained popularity during his time and was known for his imaginative works, especially "The Adventures of Tom Sawyer." Clemens adopted the pen name "Mark Twain" from his time on the riverboat, although the true origin remains unknown. His experiences on the Mississippi River influenced his career as a steamboat pilot. Clemens had a vibrant writing style that captivated readers and he remains a significant figure in American literature.