Sixteen years before the events in the first two sections, Quasimodo was laid after Mass in Notre Dame in a special bed for abandoned children. The crowd's absolute horror at the child's ugliness dissuades anybody from adopting Quasimodo until a young priest wraps him up in his cassock and carries him away. One onlooker whispers that the priest, Claude Frollo, is rumored to be a sorcerer. All his life, Frollo had been destined for the Church. He was always a remarkable student, excelling in all subjects, especially philosophy and medicine. His parents died during the plague of 1466 and Claude adopted his younger brother Jehan. Until this point in his life, Claude had loved nothing but books, but found that the love of his little brother was sufficient to fill his heart for his whole life. He devoted himself completely to his little brother and, as a result, became even more devout as a priest, eventually becoming the youngest chaplain at Notre Dame. When he saw the ugly foundling neglected by the mocking crowd, Claude's heart melted with pity, realizing that the same thing could have happened to Jehan.
The foundling's ugliness only increased Claude's compassion, and he vowed to bring up this boy for the love of his brother, calling him Quasimodo. This name both commemorates the day on which he found him and expresses the incomplete state of the poor boy's figure. Cut off from the rest of the world, Quasimodo sees Notre Dame as his home, country, and universe. He is naturally drawn to the hanging set of bells and starts to sleep next to them as a child. He grows to be incredibly strong and soon can easily scale the entire cathedral facade. But he is also one-eyed, hunchback, and lame. After becoming the bell-ringer at fourteen, his beloved bells soon make him deaf and he descends into silence to avoid the ridicule of others. Even though Frollo tries to instruct Quasimodo as best he can, ideas appear twisted to Quasimodo, whose distorted imagination makes him turn to mankind with reluctance. There is nevertheless a logic to his ways: he was mischievous because he was savage, and savage because he was ugly.
All that brings him happiness are the bells. He loves them dearly, talking to them and caressing them like children. As the narrator explains, even though the bells had deafened him, mothers are often fondest of the child that has caused them the most pain. He names his favorite bell Mary, and always pities her for the violent tolling she must undergo. In fact, Quasimodo behaves like a wild animal when tolling the bells, his eyes "flashing with fire" and his mouth foaming in fury and excitement because the intense reverberation was the only thing that could penetrate the silence of his deafness.
The only thing that has more power over Quasimodo than the cathedral was Claude Frollo. He sees Frollo as an imperious father who taught him everything he knows and then introduced him to his beloved bells. No matter how harsh and curt and Frollo becomes with him, Quasimodo becomes the most "submissive of slaves." Frollo himself grows more withdrawn and morose as the years go by due to his brother Jehan's failure to follow in his footsteps. His debauchery embarrasses Claude, who turns to astrology and alchemy to soothe his pain. He begins to hide himself in a secluded tower cell of the cathedral where he can secretly practice black magic. People suspect him of being a sorcerer, but are more shocked by his utter disdain for women, even once refusing to see the King's daughter.
Quasimodo literally means "half-made," and demonstrates the Romantic movement's interest in "physiognomy," or the belief that one's outside appearance dictated one's character traits. Certain facial features belonged to a certain "type" and that type corresponded to a kind of behavior. Normally, the uglier one's appearance, the worse the behavior. Quasimodo's character adheres only in part to this rule. His name mimics his deformed figure and explains his savage, beast-like behavior. But he is also constantly humiliated, obviously during the wrenching torture scene but more subtly in the previous night's Pope of Fool's procession. In this sense, Hugo breaks with the Romantic use of physiognomy by making Quasimodo a mirror of the evil world that surrounds him and the ugliness that people see in themselves. There is a fundamental purity to his heart that is linked to the cathedral itself. Indeed, his love for Notre Dame's bells and the beautiful sound of their ringing represents his only form of communication. The whole of Paris thus ironically enjoys Quasimodo's "singing" while at the same time detesting him for his ugliness. His soul is at one with the cathedral's radiant architecture, something that the narrator feels is missing in the present: "you feel that there is something wanting. This immense body is void the spirit has departed."
Hugo further breaks with the Romantic movement's stereotypical portrayal of antagonists. Archdeacon Claude Frollo is not a straightforward evil character bent on causing pain and suffering. In fact, he is very bright and compassionate. He dearly loves his brother and does everything in his power to make him happy after their parents die. He extends the same compassion to Quasimodo, who he tries to mold into a scholar just like his brother by teaching him how to read and write. Hugo thus explains Frollo's descent into black magic through his failure to bring up both Jehan and Quasimodo. Jehan drinks and gambles all his money away, completely neglecting his studies, while Quasimodo's deafness makes it virtually impossible to teach him anything. The hunchback thus becomes both a symbol of failure for Frollo as well as a powerful tool of vengeance to wreak his frustrations out on the world. Hugo's description of Frollo's secret cell was most likely an attempt to satisfy his readers' interest in sorcery and their expectations that alchemy should be an important theme in a novel about the middle ages. In fact, these descriptions serve more to demonstrate Frollo's madness than seriously chronicle the rise and fall of sorcery.
Hugo uses this section to set up an interesting duality between Frollo's two adoptive "sons," Jehan and Quasimodo. Together, their best traits would form the perfect child. Jehan's popularity blended with Quasimodo's sense of obedience would have changed the course of Frollo's life and kept him from going insane. Nevertheless, their worst traits get the better of them, and between Quasimodo's ugliness and Jehan's moral debauchery, they symbolize Frollo's failure as a parent and as a person. Each "son" represents a different mistake by Frollo and Quasimodo's eventual murder of Jehan while defending La Esmerelda also foreshadows Frollo's eventual self-destruction.