Young Jack serves as the central protagonist. He lives in a forest home with his animal companions Barnaby Bear, Dinah Dog, Squeeker Mouse, and Phineas Fox, who form his primary social circle and trusted allies.

Jack demonstrates self-sufficiency and mechanical aptitude, owning and operating a vehicle resembling a Ford Model T that serves as his regular transportation, even within his dwelling. His inherent adventurousness and competitive spirit drive him to impulsively challenge Allegra to a race upon seeing her flying machine. After losing, curiosity overcomes caution, leading him to accept her offer of a ride, inadvertently initiating the core conflict.

Jack exhibits significant loyalty and protective instincts toward his friends. Witnessing Squeeker Mouse transformed into a harpy by Queen Auriana's machine motivates his escape from the castle and fuels his subsequent actions. His protective nature extends to rescuing Allegra after she is punished and exiled to the ice caves by the queen, despite her previous antagonistic role, demonstrating a capacity for empathy and forgiveness.

Facing the witch's domain requires Jack's resourcefulness and courage. He navigates perilous situations within the castle, including hostile flora and the harpy-transforming machine. His leadership is evident as he coordinates efforts with his animal companions during confrontations. A pivotal moment involves pursuing the queen onto her airship after the destruction of her crystal globe power source. His actions contribute directly to the witch's defeat and the liberation of the transformed children.

Jack's character development involves confronting escalating dangers while maintaining his core values of friendship and kindness. His journey transitions him from a carefree existence into a figure instrumental in overcoming tyranny and breaking a curse. It culminates in celebrating the restoration of the harpies, including Allegra and Harvey, to their human forms following the queen's demise.