Along with Huck, Jim is the other major character in the novel and one of the most controversial figures in American literature. There are several possibilities in terms of the inspiration for Jim. Twain's autobiography speaks of Uncle Daniel, who was a slave at his Uncle John Quarles farm. Twain described Uncle Daniel as a man who was well known for his sympathy toward others and his honest heart. Another possible inspiration for Jim came from Twain's relationship with John Lewis, a tenant farmer at Quarry farm. In a letter to William Dean Howells, Twain recalled how Lewis had once saved his entire family when a horse-drawn carriage broke away on the farm. Lewis had corralled the horse and forever earned the respect of Twain, who also praised Lewis' work ethic and attitude. Several critics have also suggested that Jim was modeled after Twain's butler, George Griffin, who was a part of Twain's staff during the years that he was writing Huck Finn.
In the beginning of the novel, Jim is depicted as simple and trusting, to the point of gullibility. These qualities are not altered during the course of the novel; instead, they are fleshed out and prove to be positives instead of negatives. Jim's simple nature becomes common sense, and he constantly chooses the right path for him and Huck to follow. For example, when Huck and Jim are on Jackson's Island, Jim observes the nervous actions of birds and predicts that it will rain. Jim's prediction comes true as a huge storm comes upon the island. The moment is an important one, for it establishes Jim as an authority figure and readers recognize his experience and intelligence. Jim's insight is also revealed when he recognizes the duke and the king to be frauds. Like Huck, Jim realizes he cannot stop the con men from controlling the raft, but he tells Huck that "I doan' hanker for no mo' un um, Huck. Dese is all I kin stan'."
Jim's most important quality, however, is his "gullible" nature. As the novel progresses, this nature reveals itself as complete faith and trust in his friends, especially Huck. The one trait that does not fluctuate throughout the novel is Jim's belief in Huck. After Huck makes up a story to preserve Jim's freedom in Chapter 16, Jim remarks that he will never forget Huck's kindness. Jim's love for Huck, however, extends past their friendship to the relationship of parent and child. When Huck and Jim come upon the dead man on the floating house, Jim warns Huck not to look at the man's face. The gesture is kind, but when readers learn later that the man was Pap Finn, they realize the affection Jim has for Huck. Jim does not want Huck to suffer through the pain of seeing his dead father, and this moment establishes Jim as a father figure to Huck.
Jim's actions, no doubt, are partly a result of his inability to distance himself from the society in which he has been conditioned. His existence has been permeated by social and legal laws that require him to place another race above his own, regardless of the consequences. But as with Huck, Jim is willing to sacrifice his life for his friends. There are countless opportunities for Jim to leave Huck during the tale, yet he remains by Huck's side so the two of them can escape together. When Huck and Jim become separated in the fog, Jim tells Huck that his "heart wuz mos' broke bekase you wuz los', en I didn' k'yer no mo' what bcome er me en de raf'." Jim's freedom, then, is not worth the price of Huck's life, and readers are constantly reminded that Jim would readily risk his own life to aid Huck. When Huck is taken in by the Shepherdsons, Jim waits in the swamp and devises a plan where both of them can continue down the river. Moreover, when Jim has the chance to be free at the end of the novel, he stays by Tom Sawyer's side, another example of his loyalty. Jim's logic, compassion, intelligence, and above all, his loyalty toward Huck, Tom, and his own family, establish him as a heroic figure.