Jack Skellington

Jack is generally a tall, vivacious, charismatic gentleman, a stark contrast to his undead status, and is fond of grand theatrics, which is likely a significant part of what makes him the best at his trade. He is quick and eager to make new friends, but on that note seems to assume (often incorrectly) that others are the same. Although kind-hearted, Jack has a tendency to be self-absorbed and more than a little oblivious, failing to notice both Sally's affections and Santa Claus's apparent dislike of him. He has a tendency to become fascinated with an idea to the exclusion of all others. Jack also appears prone to mood swings, wherein he becomes depressed at a failure only to become enthusiastic when a novel idea inspires him.

Sally

Sally is a rag doll-type character, with detachable limbs stuffed with fall leaves. She was created by Doctor Finklestein, Halloween Town's resident mad scientist. Their relationship is rather tense, as Finklestein insists on keeping Sally under lock and key, under the pretext of protecting her from the excitement of the outside world. However Sally is restless, and is intrigued by the wonders of the outside world. It is this restlessness, or, more specifically, this desire for something better in her life, that draws her to Jack Skellington. In the beginning of the movie, she idolizes and admires Jack much like any of the other female members of Halloween Town; however, she quickly discovers that they are connected by the desire for something more in their lives, and her feelings for him intensify.

Oogie Boogie

Oogie's life revolves around gambling, where of he is an enthusiast and prone to bet other characters' lives. He is also implied to be "The Shadow on the Moon at Night", as the shadow shown on the moon was an exact replica of him. Ironically, he is a poor gambler and often resorts to cheating. He is also somewhat lecherous, which is evident when he is easily distracted by Sally's detached leg. According to Lock, Shock, and Barrel, as well as some of his deleted song material (which is included in the soundtrack version), he is also very skilled at making a concoction known as Snake and Spider Stew, which often includes the bodies of prisoners captured by the trio thus meaning he is carnivorous.

Doctor Finklestein

Doctor Finklestein is the mad scientist of Halloween Town, and lives in a large observatory with his living ragdoll creation, Sally, and his hunchbacked assistant Igor. James Whale's Frankenstein is quoted in Finklestein's line "I made you with my own hands", which is ironic as Finklestein's body appears to be largely if not entirely artificial. Unlike Frankenstein, who takes no responsibility for his creations and disowns them almost as soon as they are completed (much like the original Dr. Frankenstein), Finklestein takes full responsibility over Sally and acts as an over-protective father, and in some ways an overbearing husband (thus explaining Sally's attempts to run away) by keeping her under lock and key under the pretext of sheltering her from the world.

Mayor

He is the mayor of Halloween Town (as his title suggests), and is depicted as a short, fat man wearing an impossibly tall top hat, a spider bolo tie, and a ribbon of office that says "Mayor" on it. His cone-shaped head has two faces. One face is flesh-colored, rosy-cheeked, and smiling; the other face is pale, white, and frowning. Depending on the Mayor's mood, his head will swivel around to display the appropriate face with a loud clicking sound; the other face, when not in use, has its eyes closed and is considered dormant. This split personality is likely inspired by Dr Jekyll and Mr Hyde, and is a literal interpretation of the phrase "two-faced politicians".

Lock, Shock, and Barrel

Lock, Shock, and Barrel are a group of young, mischievous trick-or-treaters. They usually work as Oogie Boogie's 'henchmen' but don't often listen directly to his orders. They wear masks, despite them being almost exactly the same as their real faces. In the movie, Lock was voiced by Paul Reubens, Shock was voiced by Catherine O'Hara, and Barrel was voiced by Danny Elfman.

Santa Claus

Santa Claus (or Sandy Claws as Jack calls him) is the leader of Christmas Town. When Jack stumbles upon the town, he becomes mesmerized with the holiday and he tries to bring Christmas to Halloween Town. In order to do so, Jack orders Lock, Shock, and Barrel to kidnap Santa on Christmas Eve so he can be informed that he can take the year off as Jack will fill-in for him this year. The three then take Santa to Oogie Boogie where the holiday figure's life is threatened. A last minute rescue helps save not only Santa, but the entire holiday of Christmas as well.

Zero

Zero is Jack's faithful ghost-dog who floats about freely and follows Jack wherever he goes. His nose also doubles as a bright light. This of which he uses to light the way for Jack's Christmas sleigh, in a Rudolph the Red Nosed Reindeer fashion.

Source: Wikipedia