J. Reuben Clark, Jr. (1871-1961) was a member of the Church of Jesus Christ of Latter-day Saints, attorney, diplomat, and ecclesiastical leader in Utah.

Joshua Reuben Clark, Jr. was born September 1, 1871 in Grantsville, Utah. He entered Latter-day Saints' University in 1890. Graduating in four years, Clark then attended the University of Utah, receiving a bachelor's degree, and Columbia University, receiving a law degree. He married Lucine Annetta Savage on September 14, 1898 in Salt Lake City, Utah, and they raised four children together. He served as Under Secretary of State to President Calvin Coolidge in 1928 and as ambassador to Mexico from 1930–1933. In 1933 Clark was asked to serve as the second counselor in the First Presidency of the Church of Jesus Christ of Latter-day Saints to President Heber J. Grant, later becoming first counselor in 1934. After Grant's death in 1945, he remained as first counselor in the First Presidency under George Albert Smith. When Smith died in 1951, he was called by David O. McKay as second counselor in the First Presidency, returning to the position of first counselor in 1959. He remained in this role until his death.

J. Reuben Clark, Jr. passed away on October 6, 1961 in Salt Lake City, Utah.