A good story has a protagonist, goals, and opposition. Opposition includes obstacles and forces of nature, but typically opposition also takes the form of a character. Sometimes the opposition is another protagonist, leaving the audience to choose who they want to root for, but many stories include at least one villain, a character that is definitively “wrong”. Villains can be narrative or mechanical.
I think if we talked about some of our favorite characters, and why we liked them, each of us would cite different reasons, but I also suspect that there may be an underlying principle or two that explain why we like specific characters, in general.
Background information is a tricky aspect of storytelling. Background information is one or more details that don’t seem relevant or important in the moment, but as the story progresses audiences work to collect and combine the different pieces of background information, gradually developing a greater understanding of who a character is.