While the duke and dauphin seem to be two bumbling idiots, their cruelty can be seen in the fact that they

are threatening jim's status.
are trying to murder the drunk.
attend revival meetings.
run off with all the money at the revival meeting

While the Duke and Dauphin seem to be two bumbling idiots, their cruelty can be seen in the fact that they continually...

run off with all the money at the revival meeting

These two characters are part of The Adventures of Huckleberry Finn.  They were a pair of con men whom Huck and Jim rescued. The older man claims to be the “dauphin,” the son of King Louis XVI and heir to the French throne. He is around 70 years old.  The younger man claims to be the usurped Duke of Bridgewater. He is around 30 years old. These con men carry out a number of increasingly disturbing swindles as they travel down the river on the raft.