This is a great question and I am glad that people are studying the Russian / Greek Orthodox tradition. Patriarch Nikon was born on May 7, 1605 with the name of Nikita Minin. He was the seventh patriarch of the Russian Orthodox church and he was most famous for two actions, which occurred under this leadership.
First, he was a reformer of the church. In other words, he wanted to bypass tradition and get back to the orgins of Christianity. For this reason, he consulted a number of scholars and went back to the basics of Greek tradition. He called several synods and rewrote the service books, which were central to the life and worship of the church. He got a lot of criticism for this and was seen as ruthless in his aims.
Second, his actions, not surprisingly lead to a schism within the church and he was exiled and deprived of all his sacerdotal functions. But his reforms remained.