In the original Russian version of the Night Watch series, I believe the heads of the Moscow Night and Day Watches are called Гесер and Завулон respectively. (I don't actually have a copy of any of the books in Russian, but I've picked up this information from DVK's answers about the books, in which he includes both Russian text and his own English translation.)
In the English translations I've been reading, the names are rendered as Gesar and Zabulon, although a more literal transliteration of the above names written in Cyrillic would be "Geser" and "Zavulon". What is the reason for this deviation from a letter-by-letter transliteration? As far as I can tell, "Gesar" and "Zabulon" are no easier to pronounce in English than "Geser" and "Zavulon", nor is there any hidden meaning in any of these names which is apparent to the English-speaking eye.
Why were their names translated to Gesar and Zabulon rather than Geser and Zavulon?