Answer:
Cyrus the Great (600-530 BC) was the founder of the "Persian Empire".
They call him "the Great", because he literally created the largest empire the world had ever seen, may be to this day; the "Persian Empire" expanding from border of China and Indus River in the east, to Greece and Egypt in the west.
But, it's not only the size; the Empire was in fact, the first multi-state and multi-cultural society in the history of the World. He based his Empire on the concepts of freedom and tolerance and respect to "Human Rights". He declared the First Declaration of Human Rights after the peaceful conquest of Babylon in 539 BC, by freeing the captives and the slaves.
He was a character that even his enemies loved him, in deed, he has had a great influence in the history of the World in general;
as according to Prof. Patrick Hunt: "If you are looking at the greatest person in the History who has affected the World, 'Cyrus the Great' is one of the few who deserves that epithet."
Also Prof. Richard Nelson Frye says:
"it was no accident that Xenophon chose Cyrus to be the model of a ruler for the lessons he wished to impart to his fellow Greeks."
The various accounts and documents that have revered Cyrus as a distinguished figure are as follow;
1- the "Cyrus Cylinder" made by Babylonians as a gratitude to Cyrus's mercy on them.
2- the "Verse Account of Nabonidus" and the "Nabonidus Chronicle"
3- several instances in the "Bible" and "Quran"
4- the records of the ancient historians such as "Herodotus", "Xenophon" and "Plutarch" and many other ancient and modern historians, scholars and individuals.