"Mark Twain," a river measurement meaning "12 feet deep," was the pen name of Samuel Langhorne Clemens, who died this day, April 21, in 1910. Growing up along the Mississippi, he left school at age 12 and became a printer's apprentice when his father died. He piloted steamboats, but the War Between the States suspended all river traffic. Famous for such works as "Adventures of Huckleberry Finn" and "Tom Sawyer," he was responsible for talking Ulysses S. Grant into writing memoirs of the Civil War. In his classic style, Mark Twain remarked: "If the Ten Commandments were not written by Moses, then they were written by another fellow of the same name."