The president of the Mormon Church is called the “Prophet, Seer, and Revelator,” or the Living Prophet. Mormonism teaches that he, and he alone, receives direct revelations from God for the entire church. These revelations take precedence over written scriptures, because they are the most applicable to life in today’s world. The presidency is a lifetime position. The apostle with the longest tenure would be next in line after the death of the current living prophet who is Thomas S. Monson.
“Our greatest safety lies in strictly following the word of the Lord given through His prophets, particularly the current President of the Church. The Lord warns that those who ignore the words of the living prophets will fall. He promises great blessings to those who follow the President of the Church.” (lds.org)