Howl is a young, handsome man with bright blue eyes and hair that reaches below his chin. At the beginning of the film, his hair is blonde, but because of an incident while Sophie is cleaning Howl's bathroom, he briefly comes to have orange hair, before it finally turns black through his curse. In the novel, Howl has natural black hair.
Throughout the movie, he is seen wearing a plain white shirt and dark pants, with a plaid coat in red and a blue-ish shade of grey, which has yellow rims and sleeve ends, though Howl barely uses the sleeves at all and instead lets the coat loosely hang on top of his shoulders. Additionally, he wears a pendant around his neck.
At other times, he is shown making use of his magical abilities by turning himself into a bird-like creature. His body is then completely covered in black feathers, the only space not affected being the main part of his face. Two black broad wings are shown either on his back or in the place of his arms when he uses them to fly.
At the beginning of the movie, Howl is known as rather flamboyant and rumored to have a wicked personality. A rumor that has begun to spread among the residents of Market Chipping even say that he is searching for beautiful, young women whose hearts he may steal and subsequently eat, or that he will devour their souls. He appears rather vain, as well as confident, and does not really seem to care about a lot of others besides himself. Unlike these rumors, he is kind enough to let Sophie clean the castle.
As time goes on, his actual personality comes to light, which is that of an endearing, charming and intelligent young man, who, unfortunately, has a tendency to be stubborn and dishonest, as well as to become secretive when it comes to his own life. He commonly avoids getting involved in uncomfortable situations or those which require his committed participation. His vanity is also a very distinct trait, as he is easily irritated if something about himself looks off.
Howl Jenkins was born to an ordinary family in modern-day Wales. However, he himself was anything but ordinary. Gifted with a natural talent for magic, he began studying it. Even in college, he wrote his thesis on magical spells and charms, and joined a group of other gifted magicians on Earth.
In Wales, Howl had a habit of going out with girls and then jilting them. In an attempt to hide from three angry rugby players whose sister he had jilted, he cast a spell that opened a portal to another land, Ingary, where he moved almost permanently. Still young, he took up tutelage under Suliman. He became her last pupil, and one of her favorites (and best). His natural gift for magic showed, and he was quite powerful. He was in the same league as the Witch of the Waste. Howl is a wizard in the land of Ingary and he has several names; he is known as Wizard Howl in Market Chipping, "Wizard Pendragon" in the capital Kingsbury, and "Jenkin the Sorcerer" in lower-class Porthaven.
One night on the Porthaven Marshes, Howl caught a falling star named Calcifer and made a contract with him. He gave his heart to the creature, binding them together, and allowing Calcifer to live for he felt sorry for him, while boosting his own magical power. After doing so, Howl quit his apprenticeship and became a hermit. He dyed his hair and spent all his money on make-up and clothing, and spent his days wooing young ladies until they fell in love with him, and then jilted them. During this time, Howl found Michael Fisher sleeping on his doorstep, and invited him in. Howl was impressed by Calcifer's reaction to Michael. Though he never explicitly told Michael he could stay, Howl allowed him to live in the castle, eventually making him his apprentice. Also during this time, Howl courted and then dumped the Witch of the Waste, who put a curse on him. Howl occasionally did work for the King's army, but avoided contact with them as much as possible.
Sophie meets Howl for the first time when he rescues her from soldiers who are sexually harassing her by calling her 'Sweetheart' and apologizing for being late and saying he was looking 'everywhere' for her. He further casts a spell on them which forces them to march off. Howl then escorts Sophie to her younger sister Lettie's bakery, being followed by The Witch of the Waste's Blobbmen, he flies into the air, landing on the roof of the bakery.
Novel - Howl's Moving Castle
It is during one of his outings to find a young woman that he first meets Sophie. Howl first meets Sophie on May Day in Market Chipping before the Witch of The Waste casts an aging spell on her. Days later he returns to the Castle and is surprised to find an old woman cooking bacon on Calcifer. Despite Michael and Calcifer's complaints, he allows Sophie to clean the castle, though he stops her from cleaning his room. Although he has been gathering clues about Suliman's disappearance, Howl is concerned the King wants him to find Prince Justin. He gets Sophie to pretend to be his mother but the king is more impressed than annoyed, and hires him as Royal Wizard. The very same day, Mrs Pentstemmon is killed by the Witch of the Waste. Howl is grieved and vows to attend Mrs Pentstemmon's funeral no matter what.
Howl battles with the Witch of the Waste after attending Mrs Penstemmon's funeral. Now that the Witch knows he lives in Porthaven, he decides to move the castle to escape. Taking Michael and Sophie's wishes into consideration, he takes the hat shop in Market Chipping so Michael stays close to Martha (his love interest), and orders Calcifer to find a nice house with lots of flowers for Sophie. Howl helps in the shop and discovers the dog is a bespelled human. When Sophie admits that she knew about it he is furious with her. He restores the bespelled human to his human form and suspects he is made of Wizard Suliman and Prince Justin's body parts. Howl is stunned and terrified at this realization; he was counting on Wizard Suliman being alive.
On the night before Midsummer's Day, Howl goes to Wales for a Rugby League Reunion and gets himself drunk out of fear. He uses Sophie to get information out of him, which Sophie is later furious about. On Midsummer's Day, Howl arranges for Sophie's family to visit, to keep Sophie out of trouble. When Sophie falls into the Witch's trap, he goes into the Waste to rescue her. There, he finds the Witch and the scarecrow battling, and Howl kills the Witch. After hearing that the Witch's fire-demon has entered the Castle and touched the guitar, Howl raises a wind to bring himself and Sophie back to the Castle quickly to apprehend the demon. On the way, he finally explains his motives to Sophie.
His honesty seals his fate and in the Castle the Witch's fire demon, in the shape of Howl's nephew's English teacher, gets hold of Calcifer and squeezes the heart Howl had given Calcifer to keep him alive. Howl collapses but Sophie saves him by giving him his heart back. After breaking Howl's and Calcifer's contract, Calcifer breaks the spell on Sophie and Sophie returns to her true age. Howl destroys the Witch's fire demon, which restores Suliman and Prince Justin to their true forms, and asks Sophie to marry him.
Novel - Castle in the Air
It is a year later, and Sophie and Howl have married, and are expecting a child. While working on a divining spell for the King, Howl discovers that a djinn is going to steal the moving castle. He sends Michael and the new apprentice away, and wants to send Sophie away as well but she refuses to go. They argue about that, and while they are arguing the djinn arrives. Howl turns Sophie into a cat, and she is thrown out of the Castle. He tells Calcifer to save himself because the djinn is too strong for either of them. Howl is still in the Castle when the djinn comes, and Howl is turned into a genie by the djinn.
Howl is cursed so that he is unable to tell anyone that he is under a spell and no one is able to recognise him. Both Howl and Calcifer at some point find themselves in the hands of Abdullah, a carpet merchant, who has also lost his true love to the djinns. Howl is forced to grant a wish each day to Abdullah, although Howl uses his powers to cause as much trouble for Abdullah as possible. He later encounters the cat Sophie, who is named Midnight by Abdullah's companion the soldier, and finds that she has given birth to Morgan, who is a kitten. When Morgan is turned back into a baby, the Genie takes him to the castle in the air so he can keep an eye on him. Once the djinns are defeated, the Genie is turned back into Howl and he is reunited with Sophie, Morgan and Calcifer.
I've had enough of running away, Sophie. And now I've got something I want to protect. It's you.
- —Howl to Sophie Hatter