I don't know how anyone could leave this Dude out of a list of The Dudes of History. This guy spent his time tooling up and down the Mississippi River. Managed to stay out of the Civil War by heading of to San Francisco.
Wrote about such dudely characters as Huckleberry Finn and Tom Sawyer. Managed to make a living writing, and traveling around the world talking to people. How much more Dudish can you be?????
He seems to take nothing seriously, even his own death, which makes him a dude.