Who are the duke and the dauphin?

The duke and the dauphin are introduced in this sections reading. Huck invites these two mysterious characters onto his raft. One introduces himself as the duke of someplace in England and the other as a dauphin. One claims to speak French, which he actually doesn't, which proves Huck's point from his earlier arguments with Jim. Jim, curiously, instead of being defiant, accepts that the character speaks French. However, his French is fake. Soon, we find out that the duke and the dauphin are actually two scam artists.