As you might gather from the title, David Copperfield is the hero of our novel. But he's not only our hero and central character. He's also our narrator. David is looking back on the events of his own life. This is true even in episodes when David doesn't play a very large role in the action – when Mr. Peggotty recounts little Emily's suffering, when Mr. Micawber faces down Uriah Heep, or when Mr. Dick brings Doctor and Mrs. Strong back together, for example. Throughout the novel, David's commentary totally influences everything we think and feel about the events unfolding.
David is literally all over this novel: he really draws our attention to the overpowering influence of the narrator to shape the reader's perception of his characters. At the same time, even if David is everywhere in David Copperfield, he often takes a back seat to the most memorable characters of the book – Uriah Heep, the Micawbers, Miss Betsey Trotwood, and so on.
David becomes the focal point through which we see a wide selection of mid-nineteenth century character types: tyrants like Mr. Creakle and Mr. Murdstone, weak-willed women like Mrs. Copperfield and Dora Spenlow, angels in the home like Agnes Wickfield and Mrs. Strong, and hardworking social climbers like Tommy Traddles or the evil Uriah Heep. But by becoming the lens through which we see all of these other people and their social troubles, David often goes out of our focus. We are so close to David that it's tough to remember that he is a fictional creation just like all of the weird, unlikely figures he meets throughout the book.