"Czar" is an English
transliteration of the Russian
word Царь, the name given to the supreme monarchs of Russia
from the assumption of the title by Ivan IV
("The Terrible") in 1547
until the overthrow of the monarchy by the Bolsheviks
. The word derives from Latin Caesar
(via Old Slavonic Tsesar
), and in this sense is akin to German Kaisar
and Polish Car
The best English transliteration of the word Царь is actually "Tsar" and indeed that spelling is closest to the actual Russian pronounciation of the word, which is /tsar/. "Czar" entered the English language via German political writings by analogy to the Latin spelling, but that spelling has never been used in any Slavic language. The first usage of the spelling "Czar" was apparently Austrian diplomat Baron Sigismund von Herberstein's 1549 tract Rerum Moscoviticarum Commentarii ("Notes on Muscovite Affairs"), an important early study on Russian politics.
In modern English usage, both "Czar" and "Tsar" are considered correct spellings (and even the blend "Tzar" is acceptable), but in recent years scholars and historians have come to use "Tsar" exclusively when referring to Russian monarchs. Meanwhile, "Czar" has become the standard spelling when referring to some kind of expert or leader in a given field, as in "drug czar," "economics czar," or "porn czar."
With the exception of Russian speakers and pedants, the English word, no matter how it is spelled, is pronounced /zar/ with a "z" rather than the Russian "ts".