Based upon the New Testament model of Christ’s twelve apostles, it was an ecclesiastical body formed in 1835. Members were originally chosen and ordained by the Three Witnesses to the Book of Mormon. This quorum was originally equal to the First Presidency (3 men), the Seventy (70 men), and High Councils (local bodies of 12 men), all of whom were considered to equally hold the keys over the church. Upon the death of Joseph Smith, his successor, Brigham Young, changed the way the quorums were organized and made this quorum superior to all others. They are currently considered to exclusively hold “all the keys” in the LDS church, and the senior (longest-serving) member automatically becomes the president of the LDS church upon the death of his predecessor.1
1 A Man Without Doubt, 181.