Nikon was born a peasant and rose through the ranks of the Church to eventually become its head. He was strong-willed and zealous and had great ambitions for reform. Russia was coming back into contact with other Orthodox Churches, as well as the churces of the rest of Europe, and Nikon wished to update the rituals of the Russian Church to match the others. Thus innovations such as crossing oneself with three fingers rather than two were made mandatory.
These reforms lead to great turmoil, however. Many Russian believers saw Nikon's reforms as a betrayal of the Russian Church. The reforms coincided with a great plague in 1654 and Russians were also greatly concerned about the upcoming year 1666 which many considered the year of the apocalypse. These Old Believers were declared to be criminals by the Tsar Alexei, but many of them still refused to conform.
Nikon's reforms were put to a general Church council. The reforms were upheld, but Nikon was not. It was ruled that his assertion that the Patriarch was the equal of the Tsar was heretical, and Nikon was deposed and sent into exile in a monastery of Northern Russia.