Since the LDS Church's founding by Joseph Smith in 1830, it has been led by a man considered "prophet, seer and revelator." Mormons view their prophet/president as God's only spokesman on Earth, the only one authorized to direct the church's affairs and receive revelation.
After Smith was killed in 1844, the mantle of leadership was passed to Brigham Young, the senior apostle in the Quorum of the Twelve Apostles. Since then, the man named as president is always the longest-serving member of the Quorum of the Twelve Apostles, which inevitably means LDS leaders don't get the position at a young age.
Such men often faced physical and mental disabilities that come with age. Sometimes God's spokesman couldn't even speak.
Starting in 1981, Hinckley shouldered much of the work for three aging Mormon presidents (Spencer W. Kimball, Ezra Taft Benson and Howard W. Hunter) who became unable to fulfill everyday duties. But he had to be careful not to act as if he were usurping the prophet's place.
During Benson's decline, Hinckley constantly reassured the faithful that the prophet - though not appearing in public or going to the office - ratified every major decision. At the same time, Hinckley was clearly helping members to re-think their assumptions about church leadership.
In 1992, he described the hierarchy's "back-up system," which allowed the other men to step up.
"When a man is ordained to the apostleship and set apart as a member of the Council of the Twelve, he is given the keys of the priesthood of God," Hinckley said. "Each has the keys but is authorized to use them only to the degree granted him by the prophet of the Lord."
But Hinckley never declined.
His mind was clear to the end. He was at work on Friday, doing what he had done for the past seven decades - making decisions and directing affairs for the church he loved and to which he had devoted his whole life.