The emperor Koryfos the Great is the very first person referred to by name in Deep Secret, although it's not clear exactly where he was emperor of, or when, or what he will have to do with a book set at a fantasy fiction convention.
The narrator, Rupert Venables first describes the significance of the Infinity symbol and its relation to both the multiplicity of worlds, and the Koryfonic Empire, which lies at the midpoint between the worlds with magic and the worlds without. Apparently this Koryfos the Great ruled some two thousand years previous, for only 20 years, but he conquered multiple worlds, starting from the magical side of things and moving towards the unmagical. Those in the Empire have regarded his reign as the Golden Age of their empire, and erected numerous statues of him.
Rupert has the opportunity to look at several of these statues when he is summoned from his own world, Earth, to the Koryfonic capital to attend a judicial proceeding as the attendant Magid. He describes a place, and a process, full of oppressive ceremony, impressive architecture and ornamentation, and a short, dumpy little Emperor who turns out to be prosecuting his eldest son for the crime of trying to find out who his parents were. Apparently this is against the law for royal heirs, and apparently the young man is guilty. Rupert is disgusted by the whole thing, especially when the young man is executed on the spot by his own father.
When the awful little Emperor is himself killed shortly thereafter, Rupert is roped into participating in the search for the Imperial heirs, and it is one of the major themes and plots of the entire book. And because so much of the quest is about events and personalities in the Empire, the name of Koryfos keeps coming up again and again, with more being contributed all the time until by the end of the novel it's almost as if we knew him as a living character.
The most fascinating details about Koryfos are left until the climactic events at the end of the novel, and they are truly worth waiting for.