1) Variation on the term "dunkel" which means dark in German.
2) A last name used to describe only the most epic and powerful of human beings. The name is so legendary that people fortunate enough to be born with this surname are rarely called by their first name, instead adopting Dunckel as their most common moniker.
Thus did Dunckel smite down with his mighty fist those who stood in his way. And the children cried out with joy, and the women swooned, and everything was right with the world.