The duke and the dauphin, and even Tom Sawyer, often represent the savagery of civilization. All three characters use Jim and Huck for their own personal gain. The following quotes are some examples:
The duke says the following when they discover Jim is a runaway. They decide they can use Jim as a cover, and Jim has no say in the matter. "Whenever we see anybody coming we can tie Jim hand and foot with a rope, and lay him in the wigwam and show this handbill and say we captured him up the river..." (Chapter 20)
The Duke and the King decide to sell the Wilkes' slaves, splitting up families in the process, and reap the profits. "So the next day after the funeral...the girls' joy got the first jolt. A couple of nigger-traders come along, and the king sold them niggers...and away they went, the two sons up river to Memphis, and their mother down the river to New Orleans. I thought them poor girls them niggers would break their hearts for grief." (Chapter 27).
Tom's conversation with Aunt Sally Phelps reveals that Tom already knew Jim was freed by Miss Watson, but didn't tell anyone about it so he could have an adventure. He uses Jim and exposes him to danger and suffering just so he can have fun.
"Old Miss Watson died two months ago, and ...she set him free in her will..."
"Then why on earth did you want to set him free seeing he was already free?"
"...Why, I wanted the adventure of it; and I'd's waded neck-deep in blood to -- goodness alive, Aunt Polly!" (Chapter 42)