At 13, Samuel left school to become a printer's apprentice. After two short years, he joined his brother Orion's newspaper as a printer and editorial assistant. It was here that young Samuel found he enjoyed writing.
At 17, he left Hannibal behind for a printer's job in St. Louis. While in St. Louis, Clemens became a river pilot's apprentice. He became a licensed river pilot in 1858. Clemens' pseudonym, Mark Twain, comes from his days as a river pilot. It is a river term which means two fathoms or 12-feet when the depth of water for a boat is being sounded. "Mark twain" means that is safe to navigate.