Originally a disciple of Madame Suliman, the Royal Sorcerer of Kingsbury, he possessed outstanding talent but left her side to avoid being bound by oaths to the state and the magic academy, leading to Suliman's pursuit. Despite receiving offers to participate in the war from various nations eyeing his abilities, he hates war and refuses them, living under aliases like Jenkins or Pendragon. He confesses to being a huge coward; for instance, he is so terrified of the Witch of the Waste that he plasters his room with protective charms. He is extremely vain about his appearance. Rumors circulate that he steals the hearts of village girls. The gap between his competence and his prickly yet forgiving nature toward Sophie's mistakes is part of his charm. It is said that Howl knew Sophie's true identity even after she was turned into an old woman (pretending not to know for her sake). In battle, he often transforms into a creature resembling a bird with dark blue feathers, usually taking the form of a giant man-faced bird or an angel-like figure covered in feathers. He made a contract with the fire demon Calcifer, giving him his heart. Thus, Calcifer became the power source for the moving castle, and Howl, lacking a heart, became unable to love. His life begins to change after meeting Sophie.

After making a contract with Howl when Howl was young, he took Howl's heart and, in exchange, became bound to the castle as its power source and caretaker. On the surface, he seems cranky and claims to dislike humans—especially Howl—but he is inherently kind and helpful to others.

Howl's apprentice and housekeeper, he is also responsible for dealing with customers in Howl's stead. When handling visitors, he wears a cloak that allows him to transform into the appearance of an old man.

Though she appears to be a dignified elderly woman with a gentle face, she possesses a spiteful personality and is a sorcerer powerful enough to overwhelm even Howl. As Howl's former mentor, she holds power equivalent to a Prime Minister. She expected Howl to be her successor and has been relentlessly pursuing him ever since he left her side.

Possessing immense magical power, she was once part of the magic academy before being expelled, leading her to harbor deep hatred for Madame Suliman. She pursues Howl and Sophie to claim Howl's heart and places a curse on Sophie.