The greatest person who ever lived, is the prophet Mohammed PBUH, and no one can be gratest after him.

In this world no one is great. The great ones are in Heaven.

there is a book will help you a lot : ( The 100: A Ranking of the Most Influential Persons in History ) read more , and see the list of them : http://en.wikipedia.org/wiki/The_100

no one is greatest.but there are many great persons

Nelson Mandela