What makes Mark Twain stand out?

Writing. He wrote two of the most important novels in American Literature, Tom Sawyer and Huckleberry Finn. He was known as a humor writer. Among those referred to the most are The Celebrated Jumping Frog of Calaveras County, and The Innocents Abroad. His Life on the Mississippi is still used in history classes to give a picture of the riverboat era in America before the Civil War.