Luke is a Halloweentown goblin. He seemed to have a big crush on Marnie in the first two movies. He and Marnie seemed to liked each other but it was never reveled if they got together or not, though they probably did not, seeing as how they lived in two different dimensions.
In the first movie, at age 14, he seems to be handsome jerk, but it is later revealed that he was a goblin working for Kalabar because Kalabar made him handsome. Later, after Kalabar freezes Aggie and Gwen with an evil spell, Luke helps Marnie by risking his life. All ended well, and despite being returned to his goblin form, he got a kiss from Marnie on the cheek.
In the second movie, at age 16, he is affected by the Gray Spell, but is later turned back into a goblin. He, Marnie, and Aggie run to Gort's to find it clean. He and Marnie then use a time travel spell to try and find Aggie's spellbook, but to no avail. Later he helps Marnie figure out how to reverse the Gray Spell. In the end he makes a portal spell with Aggie, Marnie, Sophie, and Dylan.
Luke is portrayed by Phillip Van Dyke the third voice of the main character Arnold from Hey Arnold in both Halloweentown and Halloweentown II: Kalabar's Revenge.