Jim protects Huck. Jim doesn't allow Huck to see his real Pap dead in the abandoned floating houseboat. Jim sacrifices himself to help save Huck's buddy, Tom, at the end of the novel. Jim gets extremely worried and panics the night Huck played the trick on him in the fog. While Jim speaks to Huck as being Jim's only real friend, all of Jim's actions and thoughts suggest that he's really looking out for Huck's best interests throughout the novel.
From the moment Huck and Jim discover each other on Jackson Island and decide to embark on their journey together, Jim is constantly looking out for Huck and acting fatherly toward him. He even uses many phrases throughout the text which reveal his paternal attitude toward Huck, such as on page 115 when he says "Laws bless you, chile, I 'us right down sho' youse dead again."
His fatherly attitude is most evident in three main examples in the novel: when he protects Huck, scolds him, and opens Huck's eyes to the horrors of racism. First, Jim protects Huck from seeing his father, Pap, dead on the abandoned houseboad. He desires to keep Huck innocent and unaware of the atrocities that occur in the world around him, much like any parent who desires to protect their child. Secondly, and most importantly, in chapter 15 Jim scolds Huck when he discovers that Huck has lied to him. Jim, a runaway slave, scolds Huck and makes him own up to his mistake by saying, "Dat truck dah is trash." then, after about 15 minutes, Huck, a formerly racist white boy, realizes his mistake and apologizes to Jim. Finally, Jim is a father in that he teaches Huck about how to strip away his racism. Through forming a relationship with Huck and sharing with Huck his own family story, Jim teaches Huck that racism is wrong---and Huck eventualy decides to save Jim. Although Huck seems to come up with this idea on his own, it is Jim, his father figure, who plants the seed of anti-racist thought in Huck's head---and this is the most fatherly wisdom Jim could ever give southern adolescent in the mid 1800s like Huck.