Calcifer is a fire demon in the Castle series.It is Calcifer's magic that powers the Castle.In the English translation of the Japanese Hayo Myazaki adaptation he is voiced by Billy Crystal.
He is a fallen star who was supposed to die once he hit earth. However, he was caught by Howl at which point the two of them entered a deal. Howl gave Calcifer his heart and the two were bound by magic in a contract that wasn't helpful for either of them. Fairly quickly they realized it was a mistake and when Sophie Hatter stumbled into their home, it didn't take long for them to secretly enlist her help to break the curse. She succeded and gave Calcifer a thousand more years of life free from the contract. He, however, decides to stay with Howl and Sophie in the castle.
Howl's Moving Castle (Book)
Calcifer first appears on Sophie's first night in the castle, although his magic can be seen earlier, as he is the one shooting off fireworks on May Day. He allows Sophie to enter the castle because he can sense her ability to talk life into things, which makes her a perfect person to lift the contract between himself and Howl. Sophie agrees, on the terms that Calcifer break her spell in return, and that Calcifer drops her hints about the contract, since he isn't allowed to talk about it directly. He does tell her that he cannot move out of the hearth, as the contract binds him there, and that he does most of the strong magic like moving the castle. He also says that his contract with Howl isn't doing either of them any good.
Howl is reputed to eat the heart of pretty girls, he says to Sophie: "Don't you seriously want your heart eaten?" Calcifer comments on this a number of times: "Howl is pretty heartless, you know." Howl has gone out to court Lettie. Calcifer replies to Sophie:) "Heartless Howl is finding this lady rather tough." Sophie comments "It's heartless and pointless" in regard to Howl's courtship habits. Calcifer replies: "He's made that way," Sophie has a pain in her heart, and says to Calcifer that he won't understand because he hasn't got one, he replies: "Yes I do!", as he in fact has Howl's heart. Calcifer also says to Sophie, "I’m scared too, I will suffer, if Howl does." After Sophie asks Calcifer if he was a fallen star: "When Howl offered to keep me alive the way humans stay alive, I suggested a contract on the spot."
Castle in the Air
Calcifer has a short appearance at the end of the book. It is also revealed that he was the flying carpet.
House of Many Ways
Calcifer appears along with Sophie and Howl, who have been summoned to High Norland to investigate the Royal Family's disappearing money (Howl in disguise as Twinkle, since the King cannot call upon the Royal Wizard of another country). Later in the book, he destroys both the lubbock and the eggs as only a fire demon can destroy them.