Huck Finn is an uneducated teenaged boy. To escape the influence of Miss Watson, the Widow Douglas, and his drunken and abusive father, Huck fakes his own death. He then ends up on Jackson's Island where he finds Jim. The two of them travel together down the Mississippi River on a raft. His interactions with Jim along with his experiences on the way help Huck to mature and recognize some deep-seated problems in humanity. He comes to recognize that Jim deserves his freedom and is willing to go against society and follow his own conscience to help Jim obtain it.
Jim is a runaway slave. He leaves because Miss Watson has threatened to sell him down river, which means he will no longer see his family. Huck finds him on Jackson's Island. The two travel together, with Jim hoping to reach the North and freedom. Jim cares about and helps Huck, who comes to realize Jim should be free. In the end Jim is freed by Miss Watson.
Tom is Huck's friend who is only interested in adventure and silliness. He does not concern himself with other people's feelings and situations. He insists that everyone follow his plans. Rather than tell Jim he is free, Tom puts everyone through a bunch of shenanigans and ultimately causes himself to be injured.
Pap is a terrible father. He is also a racist and antigovernment fanatic who is altogether bitter. The only reason he shows interest in Huck is because of the money Huck has acquired. Pap is angry when he sees Huck being civilized. His abusive treatment inspires Huck to fake his own death so he can escape.
The duke is a con man, along with the king. The two come across Huck and Jim while running away from the people they have conned. They invade the raft and tell Huck and Jim that they are a duke and a king, then continue their cons. When they are finally found out and are down on their luck, they turn Jim in for reward money. Of the two the duke is more logical and sensible.
The king is a con man together with the duke. The two con men work together to trick gullible townspeople along the Mississippi River, including Huck and Jim. Of the two the king is greedier and more self-interested.
In contrast to her sister, Miss Watson, the Widow Douglas is a more gentle and patient figure in Huck's life, representing many of the positive aspects of civilization. In response, Huck feels kindly toward her although he rejects her civilizing influences. He knows she means well, but he does not want to abide by her rules.