In chapters 23-25 of The Adventures of Huckleberry Finn, what is ironic about the identity that the King assumes?
In chapter 23, the King assumes the role of the buffoon, acting as ridiculously as possible in front of the audience. If he were an actual king, he would never have agreed to play the fool, "a-prancing out on all fours, naked; and he was pointed all over, ring-streaked-and-striped" - conduct definitely not fit for royalty!
Chapter 24 gives the King an opening to become the leader of the pair of imposters. He gets as much information out of the boy as he can, learning everything there was to know about the extended Wilks family, their affairs and their neighbors. A real king would never have needed to pry to obtain such information, but a real king would never have decided to pose as a long-lost relative of the late Peter Wilks in order to get his hands on the estate he left behind.
The King becomes the spokesperson, talking "like an Englishman; and he done it pretty well too, for a slouch." The Duke takes on the role of the deaf and dumb brother, and the two proceed to work their way into the Wilks' sisters trust and confidence. Real royalty would have been insulted to have needed to go into a cellar to obtain finances to support them, but the King and Duke were more
In the final irony, when Doctor Robinson "said any man that pretended to be an Englishman and couldn't imitate the lingo no better than what he did, was a fraud and a liar," the Wilks sisters and the townspeople all believed the King and Duke in their assumed identities instead of believing the doctor.