Diana Wynne Jones is a British fantasy fiction author best known for Howl's Moving Castle, a book upon which the movie by Miyazaki was based, and the Chrestomanci series. The Chrestomanci is a character in her books, started in 1977, who is a powerful enchanter. It is his responsibility to monitor magic use in the world and is born into the position by having nine lives. There are eight other parallel worlds where each person has a parallel self. For the Chrestomanci, the other eight don't exist giving all of their power to the Chrestomanci.
Even though he is a powerful enchanter, he can't keep himself from dying (well, after he loses his lives), so another person must take his place. Most of the books have Christopher Chant and Eric Chant, Chrestomanci and successor, as the important characters. There are other very interesting parts of this fantasy world, some of which will make you think of Harry Potter. In fact, Wiki says that some of Jones' lesser known books were republished as a result of Potter's success.
Jones' recommended reading order is Charmed Life, The Lives of Christopher Chant, Conrad's Fate, Witch Week, The Magicians of Caprona and the short stories (Mixed Magics) can be read in any order after that. The Pinhoe Egg, my recent read, can be read after The Lives of Christopher Chant, however I have not yet read Conrad's Fate. The chronological order (for the events in the story) is as follows: The Lives of Christopher Chant, Conrad's Fate, Charmed Life, The Magicians of Caprona, and The Pinhoe Egg. The other short stories can be read separate from the main stories.
All in all, this is a great set of children's books about magic and fantasy that I recommend as an adult. Jones is 73 years old now and still published a novella last year. Although the first few books seemed to start slow, once I was used to the story line and her writing, it was a breeze.