President
Why are some Members in the Mormon Church referred to as "President" by other Members?
There are Branch Presidents, Stake Presidents, Elder's Quorum Presidents ... etc.
Members refer to each other as Brother and Sister. Those with certain stewardships of leadership, Branch Presidents, Stake Presidents and the President of the Church, Gordon B. Hinkley are referred to as President [last name] for the duration of their calling as a show of respect for their calling.
Members of the 12, missionaries and I believe, the Quorums of the Seventy are referred to as Elder [last name].
Bishops are also referred to as Bishop [last name].