David O. McKay: Set apart as the ninth president of the Church, with Stephen L. Richards and J. Reuben Clark as counselors. Other counselors in his administration were Henry D. Moyle (1959-63), Hugh B. Brown (1961-70), and N. Eldon Tanner (1963-70). Four others were called as additional counselors to the First Presidency: Hugh B. Brown (June-October 1961), Thorpe B. Isaacson (1965-70), Joseph Fielding Smith (1965-70), and Alvin R. Dyer (1968- 70). The precedent for additional counselors in the First Presidency was set in 1843 when Joseph Smith moved Amasa Lyman into the First Presidency and reinstated Orson Pratt in the Quorum of the Twelve.
[Van Wagoner, Richard and Walker, Steven C., A Book of Mormons, http://amzn.to/newmormonstudies]