Here is a little discussion/observation of each character.
Claude Frollo—the ambitious and compassionate man (about 35 years old, but comes across as a good bit older) whose thirst for knowledge let him astray from his calling. He is very well drawn out, for he is truly the main character of the book. His nefarious dealings in alchemy are hardly priestly, and his obsession with the Gypsy girl drives him insane. But there is much more to him than this. His devotion to his brother Jehan, to whom he can refuse nothing, his efforts to raise and educate Quasimodo demonstrate his generous heart. And here he was successful because he raised him moral and capable of love in the face of tremendous prejudice and superstition. Claude's torment when his world is torn apart by his unexpected love of Esmeralda, is poignant and protracted, agonizing for all his helplessness to stop himself. He is a man with all his underpinnings removed, and it ultimately destroys him. And yet is more difficult to feel sympathy for him than it is Quasimodo. Perhaps because he does have the respect (and fear) of the people, and his appearance is normal.
Jehan Frollo—Claude's younger brother (about 16), a student, and worthless, spoiled brat. He lacks his brother's virtues. He is immature, insensitive, irresponsible, a womanizer incapable of self-discipline. His behavior causes Claude much frustration and grief. His goal in life seems to be seeking pleasure no matter what the cost.
Quasimodo—perhaps the most well-known literary character of the middle ages. Born terribly deformed, with "an enormous wart" over one eye (Hugo is inconsistent about which eye it is in the translation I have, the first time he's described it's the right eye, the next time it's the left), Quasimodo was left at the church when he was about four years old. Only the kindness and perseverance of Claude Frollo gave him a chance. In a typical Hugo-ian twist, Quasimodo was actually left by Gypsies in the place of a little girl, Agnes, belonging to Pâquette la Chantefleurie in Rheims. This little girl we find out later was Esmeralda. After being abandoned by the Gypsies in exchange for the little girl, he was taken to the church and left up to the charitable populace. Claude took it upon himself to raise him, though it was a long time before he could speak. Claude and the church became Quasimodo's world, and he bonded to him as closely as any child to its mother. Quasimodo learned to read, and when he was 14 he was given the job of bellringer. He had already found out that the world outside Notre-Dame was hostile to him. People of the middle ages reacted to his unsightly form with fear and disgust. So when the bells deafened him, he silenced himself as well, except upon occasion. He withdrew into a silent world, alone except for Frollo and the bells he loved. His world was Notre-Dame with its gargoyles and spires, and until a beautiful Gypsy girl showed him kindness, he remained withdrawn into himself. He committed self-less acts to save her or help her, giving her his bed and his food when he had saved her from hanging, proclaiming "Sanctuary!" He attempted to bring the man she loved to her, but when he (Phoebus) refused to come, he could not bear to hurt her by saying so, and took her scorn instead. He brutally murders Jehan (and I just didn't feel at all sorry for the boy—after all, he made the mistake of laughing in Quasimodo's face, though I don't think anything could have saved him at that point,),when he's trying to defend Esmeralda from the attacking Truands. He pushes Claude over the balustrade where he eventually falls and dies. And Quasimodo ultimately sacrifices himself to be with the girl. One of the most romantic tragedies of all time. Quasimodo proved that not every hero is a handsome knight in shining armor, nor a clean and pristine soul.
Gringoire—ah, the poet and philosopher who ties many of the elements of the story together. A free soul if there ever was one. His adventures in the Court of Miracles are an education in themselves. I'm always glad to see that he survived the story, and with Djali, the trained goat as well. He also provides nearly all of the humor in the book.
Esmeralda—the 16 year old Gypsy girl, who was in fact not a Gypsy at all. She was stolen by Gypsies out of her crib when she was about a year old, and carried with her an amulet containing her only clues to her real parentage. A sweet and gentle-natured girl, she is extremely naive. With a blind determination, she refuses to ever believe the Phoebus does not love her. Ready to give all to him, she is incapable of facing the truth. Only once does she come to her senses about it, and that does not last. In addition, she cannot set aside her personal revulsion over Quasimodo's appearance. She is quite shallow. Nor can she think well enough to fool Frollo adequately so that she could escape. Her steadfast refusal to even feel pity for him, ultimately leads to her demise. I suppose it would be difficult for anyone to forgive the man who stabbed the one you loved, but a wiser woman would have dissembled and used Frollo's obsession against him, promising him things, then vanishing before ever having to fulfill them. But a wiser woman would also have seen through Phoebus' seduction, too. I thought the scene with her mother very sad and tense.
Phoebus de Châteaupers—Captain of the King's Archers, is a career soldier. He's been one long enough that he's only really comfortable with his troops, or with women of "common" status. Engaged to Fleur-de-Lys, and feeling rather trapped by this, his only interest in Esmeralda is as a pleasant diversion. He does not love her, feels no compassion for her, and could not care less about propriety. That he survives to marry Fleur-de-Lys, and meets his tragic end (according to Hugo) is amusingly ironic.
Notre-Dame Cathedral—not exactly a character, but imbued with such loving detail and personality by Hugo, I had to mention it. Hugo devotes a chapter to the church, describing the various ravages men have made upon it. There is even a chapter, "This Will Kill That," which, when I read this many years ago, was not particularly interesting, but when I read it recently, I found very insightful. This was simply a convoluted way of telling how the printing press destroyed true architecture. And how right he was! Cathedrals like Notre-Dame are a history in and of themselves. The church dominates the readers mind in the book, and it bears witness to all of the significant goings-on. Not only is it Quasimodo's universe, it is Claude's as well. Hugo has made me want to see it myself, to climb the dark narrow stair case to the bell towers and look out over Paris, imagining as he must have, the landscape of medieval Paris which he describes so well. I do no know if anyone is allowed up there now, but I'd just about give my eye-teeth to at least step within the doors!