For the scene where Judge Frollo sings "Hellfire" and sees Esmeralda dancing in the fire before him, the MPAA insisted that the Disney animators make Esmeralda's clothing more well-defined, as she seemed nude.
While Quasimodo is singing 'Out There', the camera pans over Paris and zooms in on a street. In this scene, Belle from Beauty and the Beast (1991) is seen walking and reading her book (walks out the bottom of the screen, to the right of the well), Pumbaa from The Lion King (1994) is being carried on a pole by two men (carried out of the bottom of the screen, but left of the well), and another man (in a gray-blue tunic) is shaking out the Carpet from Aladdin (1992).
The opening scene, in which Clopin sings "The Bells of Notre Dame", was originally all spoken dialogue. After two revisions, it was decided that it was too dry and boring, and so was turned into a musical number.
In the novel, Frollo is actually the Archdeacon. The filmmakers decided to change the character to a judge because they felt it would make him more sinister to have control over the city and therefore would not be questioned in his attempts to destroy the Gypsies.
According to the commentary of the DVD onto when Kevin Kline did the voice of Phoebus, the directors gave Kline a sword so that he'd portray the role. They also named the horse Achilles because it was funny to hear him say "Achilles, heel."
According to the audio commentary on the DVD, the gargoyle that resembles a warthog (which can be seen during the climactic battle atop Notre Dame Cathedral) is actually not Pumbaa from The Lion King (1994) but the actual gargoyle that can be seen in that location on the real Notre Dame Cathedral in Paris.
The Latin chants heard throughout the movie are adapted from actual Gregorian chants, including a portion of the Dies Irae music can be heard in the scene where Frollo kills Quasimodo's mother. It was part of Wolfgang Amadeus Mozarts famous last compositions, Requiem in D Minor. Tom Hulce (Quasimodo) played Mozart in the movie Amadeus (1984).
At one point, the three gargoyles were going to be all male and named Chaney, Laughton, and Quinn - the three actors who have played Quasimodo in other adaptations of the story (Lon Chaney, Charles Laughton, Anthony Quinn).
Blue and red were used to symbolize good and evil, respectively. Quasimodo's and Esmerelda's disguising cloaks are blue while the firelight Frollo is near as he plots evilly to himself reflects off his face as red.
This film was the final screen credit for veteran actress Mary Wickes, who died before finishing all her lines. A vocal "stand-in" (Jane Withers) recorded her remaining lines. Withers had to match Wickes' voice and performance so that audiences wouldn't detect the difference. She reprised the role in the sequel, The Hunchback of Notre Dame II (2002).
Directors Kirk Wise, Gary Trousdale, and Don Hahn have noted that the three gargoyles might exist only in Quasimodo's imagination and thus may well be split-off pieces of his own identity. However, most of their characteristics, including Hugo's infatuation with the goat Djali, seem unique to their manifestations when present (and there is of course the question of how the gargoyles can be moving around and even helping defend the cathedral if they are not really alive).
When supervising animator Michael Surrey (Clopin) heard the song "Court of Miracles" he noted that a portion of it was similar to "The Sorcerer's Apprentice" music used in Fantasia (1940). After this, he animated Clopin lifting up his robe to skip towards the lever after Mickey Mouse's movements.
To stay consistent to the architecture and details of Notre Dame, animators spent several weeks in and around the actual cathedral. They were given office space at the recently-opened Disneyland Paris in the interim.
This movie is full of computer animation and CGI backgrounds. All the bells appearing throughout the movie are 3D-rendered. When Quasimodo sings "Out There" and slides down the flying buttress, it appears 3D. During "Topsy Turvy", the confetti and the crowd of hundred people are digital images. While Esmeralda sings "God Help the Outcasts", the reflection of the rose window is computer-rendered. During "Hellfire", the background flames are one example of CGI. When we see the miller's home getting burned, the flames that big and appearing too fast were hard to animate traditionally, so probably the animators used computer generated images for this. When Quasimodo rappels down from Notre Dame to save Esmeralda, we can see hand-drawn animation combined with 3D scenes.
Bette Midler sang another version of 'God Help the Outcasts' for the soundtrack release. Various words are changed in this (such as instead of 'gypsy' the word 'humble' is used), in addition to these changes, the parts sung by the people in the church are not in this version and the song is also much longer.
Early on in the movie during "Out There", there is an overhead shot of Notre Dame and the courtyard from a bird's-eye view. During this shot, look closely at one of the buildings in the bottom left corner of the screen - one building has a satellite dish on it.
At the end of the film as the camera zooms out from Notre Dame cathedral, the pigeons all gather on Laverne again. She shoos them off and asks them if they ever migrate. The fact is, rock doves (the most common breed of pigeon seen in urban areas) do NOT migrate, at least not in the same sense other birds migrate. They may move from one part of a city to another, but for the most part they stay in the same area.
The film had its premiere on June 19, 1996 at the Superdome in New Orleans, utilizing six enormous screens, and was preceded by a parade through the French Quarter. The song "Someday" was sung over the credits by the group All-4-One, but the European version replaced them with the British band Eternal.
The multiplane effect was used in several scenes. When Quasimodo sings "Out There", the camera pans over Paris and seems to look three-dimensional. Additionally, the camera pans through the Parisian buildings and we see the Palace of Justice.
Supervising animator Andreas Deja really wanted to animate Esmeralda from the beginning of the film's conception, which would've been a stark departure for him - he is best known for animating villains like Gaston in Beauty and the Beast (1991), Jafar in Aladdin (1992), and Scar in The Lion King (1994). When that position went to Tony Fucile, Deja went on to supervise the animation of the titular character in Walt Disney Pictures' next animated film, Hercules (1997).
Several times during the film there are references to a war. The conflict in question was the Hundred Years' War between England and France, that engulfed all Europe from 1337 to 1453 and also involved Portugal, Scotland, Genoa, Navarra, Aragon, Bohemia, Brittany, Castille, Aquitaine, and Burgundy. Ultimately, it was won by France and the reigning House of Valois.
The trivia item below may give away important plot points.
The filmmakers considered having Quasimodo killed off, as he has in the original novel. He was originally supposed to be stabbed by Frollo, then Esmeralda regains consciousness and tries to save him by killing Frollo. Phoebus was then supposed to meet up with them, and Quasimodo's last wish was to ring the bells one last time, but then Esmeralda and Phoebus help him ring the bells as he dies. Luckily; this is not the ending that was used, because even hardcore fans of the novel agree that the ending they used instead was a more suitable ending for the theme of this film.