How did Samuel Clemens’s work as a Mississippi River pilot influence the name Mark Twain?

Samuel Clemens’s career as a Mississippi River pilot directly inspired his famous pen name. In the context of river navigation, the nautical term mark twain signifies that the water depth has been measured at two fathoms, or 12 feet (3.7 meters)—mark meaning measure and twain meaning two.12

While Clemens had used various pseudonyms earlier in his life, he eventually adopted this name permanently. Notably, Clemens also recalled envying the pen name when it was used by a senior riverboat pilot named Isaiah Sellers, whom Clemens had previously lampooned in a satirical sketch.31