At the moment there are 19 different classes that are known; Archer, Guardian, Lumberjack, Mechanic, Mason, Blacksmith and Sailor drawn up by Aaron and the Executioner, Thief, Merchant, Wizard, Hedge Wizard, Worker, Farmer, Beggar, Assassin, Traveler, Fisherman and Monk drawn up by Adam Laurie.
There are also another 7 classes which are so far unknown.
Each class will most likely be able to supply you with unique, class specific items and processes.
One guess for 'Unknown Dorf class #1' could be a Fisherman.
Since Alpha 37 Pre-Release, one random class icon is shown while starting the game.