Acting President of the Quorum of the Twelve Apostles is a priesthood calling in The Church of Jesus Christ of Latter-day Saints (LDS Church).
In general, the position of Acting President of the Quorum of the Twelve Apostles is only filled when the President of the Quorum of the Twelve Apostles is called as a counselor in the First Presidency of the church. In such instances, the man who holds this calling is the most senior apostle who is not serving in the First Presidency. Additionally, a person may be called as the Acting President of the Quorum when the actual President of the Quorum is unable to perform his duties due to ill health or other incapacitation.
The formal calling of Acting President of the Quorum has been held six times by five men: Rudger Clawson, Joseph Fielding Smith, Spencer W. Kimball, Howard W. Hunter, and Boyd K. Packer. Additionally, two earlier apostles—Orson Hyde and Brigham Young, Jr.—have acted as President of the Quorum of the Twelve Apostles when they were not the second-most senior apostle in the church, and therefore may be said to have played the role of an Acting President of the Quorum before this specific title was created by the church.
As the Acting President of the Quorum, the person with this calling performs all of the duties that would normally be performed by the President of the Quorum. Primarily, these duties consist of presiding at and conducting the weekly meetings of the Quorum in the Salt Lake Temple; making decisions about the particular assignments to be made to the members of the Quorum; and acting as a liaison in coordinating the work of the Quorum with the First Presidency, the Quorums of the Seventy, and the Presiding Bishopric.