Who /What is Byzantine emperor ?

Answer 1

This is a list of the Emperors of the late Eastern Roman Empire, called Byzantine by modern historians. This list does not include numerous coemperors who never attained sole or senior status as rulers.

The title of all Emperors listed preceding Heraclius was officially Augustus, although various other titles such as Dominus were used as well. For official purposes, their names were preceded by Imperator Caesar Flavius and followed by Augustus. Following Heraclius, the title commonly became the Greek Basileus (Gr. Βασιλεύς), which had formerly meant generally "king", "sovereign" but now was used in place of Augustus. Kings were now titled by the neologism Regas (Gr. Ρήγας, from the Lat. "Rex") or by another generic term Archon (Gr. Άρχων, "ruler"). Autokrator (Gr. Αυτοκράτωρ) was also frequently used, along with a plethora of more hyperbolic titles—with grandiloquence typically in inverse proportion to actual power—including Kosmokrator (Gr.Κοσμοκράτωρ) ("Master of the Universe") and Chronokrator (Gr.Χρονοκράτωρ) ("Lord of All Time"). The emperors of the 15th century alone were often self-styled as Basileus ton Hellinon, "Emperor of the Greeks," though they still considered themselves "Roman" Emperors.

[Note: See also the term "Byzantine" with regard to the late Roman Empire. This list begins with Constantine I the Great, the first Christian emperor reigning from Constantinople, although Diocletian before him had ruled from Nicaea and replaced the pseudorepublican trappings of the office with a straightforward autocracy and Heraclius I after him replaced Latin with Greek and began the restructuring of the Empire into themata.]

Answer 2

Go to http://en.wikipedia.org/wiki/Byzantine_empire
It has all the information you could ever need (usually)