"Though the novel is entitled The Adventures of Huckleberry Finn and the story is told by Huck, the key character in the novel is Jim"
The Adventures of Huckleberry Finn has two key characters, one is the slave Jim, the other; the protagonist Huck. Jim and Huck could each be considered the key characters for different reasons, Jim as he is the main representative of the typical slave (slavery being the most important theme of this novel) and Huck for he is the main storyteller.
Jim is an important character in The Adventures of Huckleberry Finn, and without him the novel would be ineffectual. However The Adventures of Huckleberry Finn is a novel about the adventures of the protagonist Huck, and it is more likely that the key character of this novel is Huck because we see everything from his view.
In a novel which is written as a satiric social comment upon the southern states of America Jim's role as the manifestation of slavery must be a key one. Incidents in which Jim interacts with other characters and their reactions to him are meant to symbolise the wider society's opinions on slaves and the practice of slavery.
Jim, is a heroic figure in a book whose main characters consist of liars, cheats and scoundrels. Jim always does the right thing if he can, he always feels empathy for others even if those people show no such emotions for him. The incident at the end of the novel when he saves Tom and risks what he believes to be his own freedom is a case in point.
We empathise with Jim because even though other characters suggest that his feelings are least important, whose life is lesser, whose existence is trivial, he manages to stay cheerful, and even kind to those who treat him in this manner. This quality makes him even more heroic, for he is a figure who turns the other cheek, and is kind to others no matter what. Jim doesn't lie or cheat, or steal or gamble and looks down on these activities.