Quasimodo (/ˌkwɒzɪˈmoʊdoʊ/ KWOZ-im-OH-doh, UK also /ˌkwɔːz-/ KWAWZ-; from Quasimodo Sunday) is the titular protagonist of the French novel The Hunchback of Notre-Dame (1831) by Victor Hugo. Born with numerous deformities, most notably a hunched back, Quasimodo serves as the bell-ringer for Notre Dame cathedral in fifteenth century Paris. Although his appearance causes others to treat him cruelly, he ultimately finds sanctuary in an unlikely love that is fulfilled only in death.

The role of Quasimodo has been played by many actors in film adaptations, including Lon Chaney (1923), Charles Laughton (1939), Anthony Quinn (1956), and Anthony Hopkins (1982). In addition, he was voiced by Tom Hulce in a Disney animated feature (1996); was parodied by Steve Lemme in the comedy Quasi (2023); and most recently was portrayed by Angelo Del Vecchio in a revival of the French-language musical Notre Dame de Paris.

In 2010, a British researcher found evidence suggesting there was a real-life hunchbacked stone carver who worked at Notre Dame during the same period Victor Hugo was writing the novel and they may have even known each other.

The deformed Quasimodo is described as "hideous" and a "creation of the devil". He was born with a severe hunchback, a bushy eyebrow covering his left eye while the right eye "disappeared entirely" behind a giant wart, and broken teeth, one of which protruded over his mouth. He was born to a tribe of Romani people, but due to his monstrous appearance he was switched during infancy with an able-bodied baby girl, Agnes. One character in the novel refers to him as animalistic and un-Christian, suggesting he may be the "offspring of a Jew and a sow", and thus deserving of death. After being discovered, Quasimodo is exorcised by Agnes's mother (who believed that the Romani people ate her child) and taken to Paris. He is found abandoned in Notre Dame (on the foundlings' bed, where orphans and unwanted children are left to public charity) on Quasimodo Sunday, the First Sunday after Easter, by Claude Frollo, the Archdeacon of Notre Dame, who adopts the baby, names him after the day the baby was found, and brings him up to be the bell-ringer of the cathedral. Due to the loud ringing of the bells, Quasimodo also becomes deaf causing Frollo to teach him sign language. Although he is hated for his deformity, it is revealed that he is kind at heart. Though Quasimodo commits acts of violence in the novel, these are only undertaken when he is instructed by others.

Looked upon by the general populace of Paris as a monster, he believes that Frollo is the only one who cares for him, and frequently accompanies him when the Archdeacon walks out of Notre Dame. Frollo lusts after a beautiful Romani girl named Esmeralda, and enlists Quasimodo in trying to kidnap her. (She is later revealed to be Agnes, the baby with which Quasimodo was switched.) Captain Phoebus de Châteaupers arrives to stop the kidnapping and captures Quasimodo, unaware that Quasimodo was merely following Frollo's orders. The deaf judge Florian Barbedienne sentences him to an hour of flogging and another hour of humiliation on the pillory. Phoebus ties up Quasimodo and has Pierre Torterue whip him in front of a jeering crowd. When Quasimodo calls to him for help, Frollo allows Quasimodo to be tortured as punishment for failing him. When Quasimodo calls for water, a child throws a wet rag at him. Seeing his thirst, Esmeralda approaches the public stocks and offers him a drink of water. It saves him and she captures his heart.

Esmeralda is later entangled in an attempted murder – committed by Frollo, who had stabbed Phoebus in a jealous rage after spying on Esmeralda and Phoebus having a night of passion – and is sentenced to be hanged. As she is being forced to pray at the steps of Notre Dame just before being marched off to the gallows, Quasimodo, who has been watching the occasion from an upper balcony in Notre Dame, slides down with a rope, and rescues her by taking her up to the top of the cathedral, where he poignantly shouts "Sanctuary!" to the onlookers below.

Esmeralda is terrified of Quasimodo at first, but gradually recognizes his kind heart and becomes his friend. He watches over her and protects her, and at one point saves her from Frollo when the mad priest sexually assaults her in her room. In one instance Esmeralda also sees Phoebus from the cathedral balcony and pleadingly convinces Quasimodo to go down and look for him, but Phoebus is repulsed by Quasimodo's appearance and refuses to visit Notre Dame to see her.

After an uneasy respite, a mob of Paris's Truands led by Clopin Trouillefou storms Notre Dame, and although Quasimodo tries to fend them off by throwing stones and bricks down onto the mob and even pours deadly molten lead, the mob continues attacking until Phoebus and his soldiers arrive to fight and drive off the assailants. Unbeknownst to Quasimodo, Frollo lures Esmeralda outside, where he has her arrested and hanged. When Quasimodo sees Frollo smiling cruelly at Esmeralda's execution, he turns on his master and throws him to his death from the balcony in rage.