Which persian leader do you think made the biggest contribution?

When you want to find the most important leader of a nation, it is useful to know whom the nation itself calls "the Great" - in the case of the Persians it was Cyrus the Great (he lived in the 6th Century BC) - we has the founder of the first Persian Empire. Among his contributions is that he expanded the area ruled by the Persians.

Ongoing civil wars western roman empire finally collapsed476 c.e. romulus, the last of theroman  emperors in  the west, was overthrown by the germanic leader odoacer, who became the first barbarian to rule in rome. the order that the  roman empire  had brought towestern  europe for 1000 years was no more.