Make sure you're sitting down for this: this book is not called The Hunchback of Notre-Dame.
Victor Hugo titled his novel Notre-Dame de Paris, which in French is simply "Notre-Dame of Paris." That's nothing but the name of the cathedral. Doesn't have quite the same ring to it, does it? Hugo apparently disliked the English title (source), though we can see why more people might be interested in reading a grotesque story about a bell-ringing hunchback than about a cathedral.
But what was initially a marketing move actually makes a huge difference in how we perceive the novel. The Hunchback of Notre-Dame implies, naturally, that the story is about a hunchback. Therefore, we're more inclined to see Quasimodo as the main character. After reading the book, though, you might find yourself scratching your head at how small a role Quasimodo actually plays in the greater scheme of things.
But if we take the original French title, we see the cathedral as the focal point for all of the action that revolves around it. In reality, the novel is more about a whole cast of characters whose plots intertwine. So fight back against everything you've ever heard about how Quasimodo being the hero of this book. You may be surprised at how much it changes your reading.