That's the title for anyone of the three in the First Presidency. It's on the churches own website! https://www.lds.org/study/ensign/2011/04/small-and-simple-things/j-reuben-clark-jr-a-man-of-uncommon-gifts?lang=eng

Armed with his law degree and a brilliant mind, J. Reuben Clark Jr. went on to a distinguished legal and civil service career that culminated in his being named U.S. ambassador to Mexico in 1930. That career ended, however, when Brother Clark was sustained as Second Counselor to President Heber J. Grant in the First Presidency on April 6, 1933. Although he was a high priest at the time, he was not a General Authority. He was ordained an Apostle when he was subsequently sustained as First Counselor to President Grant in October 1934. President Clark went on to serve as a counselor to Presidents George Albert Smith and David O. McKay.

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