In To Kill a Mockingbird, Harper Lee characterizes Jem Finch as being very similar to his father while also being his own person. Jem is characterized as a very morally upright, brave person, while also still being a bit young, naive, and rebellious. Throughout the story, Scout, the narrator, uses many adjectives to describe what her brother Jem is like as a person.
Early on, Scout describes her brother Jem as prideful while also pointing out that he is "respectful." Jem's pride surfaces the moment Dill begins to persuade Jem to conspire with him to try and get Boo Radley to come out of his house. Scout notes Jem's pride when she describes Jem thinking over Dill's temptation for three days in the following:
Jem thought about it for three days. I suppose he loved honor more than his head, for Dill wore him down easily. (Ch. 1)
Scout also notes that Jem finally gave in to Dill's persuasion on the third day to make Boo come out. In saying that Jem "loved honor more than his head," Scout is saying that Jem loved his pride more than he loved thinking reasonably. Since Jem doesn't want Dill thinking he is chicken, Jem becomes willing to give in to Dill's persuasion.
In this same passage, Scout also describes Jem as being a reasonably respectful person while growing up when she notes his response to Dill's taunt that Jem is scared. According to Scout's narration, Jem replies, "Ain't scared, just respectful," which shows us that Jem has been brought up to be morally inclined to respect other peoples' thoughts, feelings, and privacy (Ch. 1).
As Jem gets older, he begins spending less time with Scout and more time by himself. He especially spends time alone reading football magazines. It's at this stage in their relationship when Scout describes him as having a sense of "maddening superiority" (Ch. 14). For example, Scout considers it "maddening" that Jem should think he understands more than Scout about how worried adults can be. More specifically, at one point, Jem begs Scout not to "antagonize Aunty [Alexandra]" because Alexandra and Atticus are beginning to quarrel due to the fact that Atticus has a lot on his mind concerning Tom Robinson's trial. Scout insists "Atticus [doesn't] worry about anything" and that the trial only worries him about once a week. When Jem says the only reason why Scout thinks the trial isn't worrying Atticus is because she "can't hold something in [her] mind but a little while," whereas adults can think about things for a longer time, Scout becomes infuriated by what she calls Jem's "maddening superiority" (Ch. 14).
Hence, as we can see, Jem is described as a very complex character who is usually respectful and moral but can also be prideful and rebellious.