In "Dark Ages" Vexler impresses the king by finding a lucrative tax loophole. But, why would the king need a tax loophole, since he's the one setting and receiving the taxes?
Alternately, because the king is a subordinate king to a High King. This wasn't at all uncommon in the Middle Ages, in truth and fiction - several of King Arthur's knights were kings in their own right, for example.
