Joan Leaven is one of the characters from the first Cube film. She is portrayed by Nicole de Boer.
Leaven is a mathematics student who finds herself trapped within the Cube structure along with five other people from different walks of life. She had lived a privileged life which left her with a needy disposition, though the time she spends in the Cube turns her into a headstrong, angry young woman.
Using her mathematical skills, Leaven tries to figure out the dynamics of the Cube, but toward the end she and Worth learn that Kazan, the autistic member of the group, is a mathematical savant who rapidly performs prime number calculations in his head. Using Kazan's gift, she and Worth find their way to the Cube's exit point (which ironically turned out to be the room they started off in). Before they can leave, however, a blood-soaked Quentin appears and stabs Leaven with a broken door handle.