Who was the greatest king in the world and who killed him and why?...

This answer is highly subjective, of course, but I would
have to suggest Alexander the Great, king of the Macedonian
empire. Alexander III of Macedon (356 BC-323 BC) established one of the greatest empires
in ancient history. He was also considered one of the foremost battlefield commanders of
all time, never being defeated in battle. He was tutored by the philosopher Aristotle,
and ascended to the throne at the age of 20 following the assassination of his father,
King Phillip II, in 336 BC. In 13 short years, Alexander's empire became the mightiest
in the world. Already ruling the Greek city-states, Alexander eventually conquered the
Persian empire. His conquest of India and Arabia was never realized, and he died at the
age of 33 in Babylon. The cause of death is unknown, but it seems to have stemmed from
an intestinal
ailment.