K is the guardian of the Castle of the Prism and the figure who administers the trials of its towers.
He sets out the rules: each companion enters one tower alone and must pass the trial to obtain the gem. At the end he offers to stay or leave: “If they dismiss me, I will go.”
He has “greedy eyes”, and a penetrating look reveals “the eyes of Minos”, the judge who was defeated, hinting at a possible connection. He says he has “a little shack beside the Styx.”