The Church of Jesus Christ of Latter-day Saints
The leaders of the Church are fifteen old men titled apostles. The man who has been an Apostle for the longest time becomes President of the Church and the man who has been an Apostle the second longest is President of the Quorum of the Twelve Apostles. The President of the Church picks two Apostles to be his First and Second Counselors in the First Presidency (the First Presidency being the President and the 2 Counselors while the other 12 Apostles make up the Quorum of the Twelve Apostles). If the President of the Quorum of the Twelve is one of the Counselors, or the second longest serving Apostle is too sick to do the work that comes with being President of the Quorum of the Twelve, the longest serving other Apostle who is not in the First Presidency is named Acting President of the Quorum of the Twelve Apostles. Since Russell M. Nelson became President of the Church, Dallin H. Oaks has been President of the Quorum of the Twelve Apostles and First Counselor in the First Presidency and M. Russell Ballard has been Acting President of the Quorum of the Twelve Apostles.