The characters in novels are most likely knowledgeable about something. To convey this in a story, the writer must also be knowledgeable, though maybe not as much as the character. After all, I don’t know as much about astrophysics as my Commander José Aguire does, but I know enough to write about him.
Each of my major characters has a profile of 3 or more pages that tells who they are, what they look like, where they come from and how they got to be that way. Secondary characters get 1 or 2 pages of profile. Important organizations, such as the Exploration Corps in my novel also get some history written, which may or may not make its way into the actual story, but it’s all needed to make sure there are no overlooked plot holes, and to explore possibilities in storytelling.
For the Arcturusians I went back about six thousand years to build their culture and civilization. Only a pinch of that history made it into the first book, which is mainly told from the Earth explorers’ point of view.
The second book will deal with the first pioneers from Earth who settle on this fictional world, and much of that story will be from an alien point of view, letting more of their history enter into the story. The ground work for it is already laid in the first book.