Kalabar

Kalabar is the main antagonist in Halloweentown. He was portrayed by Robin Thomas.

Background
Kalabar is a warlock who resided in Halloweentown. He was once the boyfriend of Gwen, daughter of Agatha Cromwell. He would become furious when she chose to marry a human man from the mortal realm. At some point, he became Halloweentown's mayor. As a warlock, Kalabar possessed the ability to do magic. He was capable of casting powerful dark spells which he used on any unfortunate citizens. However, most of the town remained unaware of his dark powers, as he would transform into a shadowy monster when using them.

To nearly everyone he knew, he appeared as the kind and helpful mayor of Halloweentown. According to Gwen, he would often allow his magic to do the talking for him. However, he had a secret hatred for humans for forcing them to leave the mortal realm, and hatched a plan to convince the citizens of Halloweentown to accompany him on a journey to conquer it.

Halloweentown
Kalabar first appears walking around the town. Agatha comes to him to let him know that another citizen, a personal friend named Harriet, has undergone a severe personality change. Agatha lets him know that is past precedent holds, she will eventually disappear without a trace. Kalabar apologizes for not taking Agatha's earlier claims seriously and promises to look into the matter. Kalabar would later met Agatha's grandchildren, Marnie, Dylan, and Sophie, and would treat them kindly, likely due to them being the children of his former girlfriend.

Later on, Gwen, comes to Halloweentown to reclaim her children, who had sneaked into Halloweentown without her permission. Kalabar would encounter her when she goes to the mayor's office for help when the bus to the mortal realm is not working. He impresses her with a minor feat of magic, and the two briefly reminisce on their shared history. Kalabar then leaves suddenly, claiming to need to handle an emergency.

In reality, Kalabar goes to an abandoned theatre, where he takes the guise of a shadowy monster. He has a brief meeting with Agatha, whom he tries to convince to join him. However, she refuses and the two begin to fight. Gwen and her children arrive, having believed Agatha to be in danger. Kalabar, as the monster, is able to take advantage of the distraction to cast a spell on both Gwen and Agatha, which freezes them.

While the children take up the role of completing a spell that will defeat the demon, Kalabar readies his final plans. He takes his shadow form and confronts the townspeople. He then takes his normal form, revealing to everyone that he is the monster. He attempts to convince the people to come with him to the mortal realm to retake it from the humans. He had become bitter over their people's relocation due to a lack of human acceptance, as well as Gwen's refusal of him in favor of a human. However his plans are halted when Marnie and her siblings install a talisman that reverts the freezing spells he had cast, though he initially tries to freeze Marnie to prevent her from completing the task.

Gwen and Agatha soon arrive, and with Marnie, attempt to combine their powers to permanently vanquish Kalabar. The attempt is unsuccessful, as Kalabar is stronger. However they are successful when they add Sophie and Dylan's emerging powers to the mix. Together, their powers activate the talisman, which destroys Kalabar in a blast of light.

Halloweentown II: Kalabar's Revenge
Kalabar does not appear, but is mentioned a few times. It is eventually revealed that he had a son, a warlock named Kal, and that the two had a rocky relationship. However, after Kalabar's destruction at the hands of the Cromwells, Kal plots to complete his father's revenge.

Trivia

 * Despite his feelings for Gwen, he had a son with someone else.
 * The reason Kalabar hates humans may be due to Gwen choosing to marry one instead of him.
 * The closed captions for the first movie have his name written as Calabar; the second movie, however, explicitly has his name written as Kalabar, especially in the title.