The Japanese book covers each have the name of the title character on them. Something I noticed while flipping through the pictures of them.
The Alchemyst: Nicholas Flamel
The Magician: Niccolo Machiavelli
The Sorceress: Perenelle
and now The Necromancer: John Dee
They've gotten the Magician and the Necromancer mixed up on the two covers.
To be honest, I don't blame them. Josh being the Necromancer wasn't that obvious.
(Don't worry, I love the Japanese and everything about them. I don't mean anything negative.)