Joshua Reuben Clark, Jr. was an apostle of The Church of Jesus Christ of Latter-day Saints (Mormon Church) as well as a prominent American attorney at law and dedicated civil servant. He was a prominent attorney in the Department of State, and Under Secretary of State for U.S. president Calvin Coolidge. In 1930 Clark was appointed U.S. Ambassador to Mexico. It was while he was serving in Mexico that Mormon Church President Heber J. Grant issued him the call to return to Salt Lake City and serve as a counselor in the First Presidency. The calling came as a surprise as the sixty-one year old Ambassador had never served as a bishop or a stake president. Dutifully, J. Reuben Clark heeded the call and served nearly thirty years as a counselor to three LDS presidents.
J. Reuben Clark was born on September 1, 1871, in the farming community of Grantsville, Utah Territory (about 35 miles southwest of Salt Lake City). Clark was mostly tutored by his mother during his young years. He had not been able to attend high school, but by 1898, after four years at the University of Utah, Reuben completed all the requirements for both his high school diploma and his bachelor of science degree. He graduated first in his class and was valedictorian - in addition to having served as student-body president, managing editor of the student newspaper, and secretary to Dr. James E. Talmage, who was president of the university. 
On September 14, 1898, J. Reuben Clark married Luacine Annetta Savage in the Salt Lake Temple, with Dr. Talmage officiating at the ceremony. For the next four years he held various positions around the state as a teacher and administrator on both high school and college levels. Elder Clark then began graduate work at Columbia University. His first year's work was of such high quality that he was among the three second-year students elected to the editorial board of the Columbia Law Review. By the end of his second year he was admitted to the New York Bar. He received an LL.B. degree in 1906. He also became a member of Phi Delta Phi, a prominent international legal fraternity in which Clark remained active throughout his life. He later became an associate professor at George Washington University. Both the J. Reuben Clark Law Society and the J. Reuben Clark Law School at Brigham Young University were named in his honor. 
Three months after graduating from law school in 1906 J. Reuben Clark began his government service. Clark was appointed assistant solicitor of the State Department by Elihu Root, secretary of state under President Theodore Roosevelt. Shortly thereafter he was also named an assistant professor of law at George Washington University, where he taught until 1908. In July 1910, under the administration of President William Howard Taft, Mr. Clark was appointed solicitor of the State Department. As part of his responsibilities he represented the United States in a dispute with Chile. The king of England, serving as arbitrator, ruled in favor of the United States and granted one of the largest international awards up to that time - nearly a million dollars. Also during his solicitorship, Clark published his classic "Memorandum on the Right to Protect Citizens in Foreign Countries by Landing Forces." Secretary of State Philander C. Knox declared of Mr. Clark: "I am doing him but justice in saying that for natural ability, integrity, loyalty, and industry, I have not in a long professional and public service met his superior and rarely his equal." 
J. Reuben Clark left the State Department in 1913 to open law offices in Washington, D.C., specializing in municipal and international law. His clients included the Japanese Embassy, Philander C. Knox, the Cuban Legation, the Guatemalan Ministry, J.P. Morgan & Company, and the Equitable Life Assurance Society.
During World War I, Clark worked in the Attorney General's office. He also participated in creating the regulations for the Selective Service. In 1928, as Under Secretary of State to President Calvin Coolidge, Clark wrote the "Clark Memorandum on the Monroe Doctrine", which repudiated the idea that the United States could arbitrarily use military force in Latin America. Clark served as U.S. ambassador to Mexico from 1930–1933. Regarding his service, President Hoover said, "Never have our relations been lifted to such a high point of confidence and cooperation."
In April 1933, Clark was called to serve in the LDS Church as the Second Counselor in the First Presidency to President Heber J. Grant. In October 1934, Clark was ordained an apostle and member of the Quorum of the Twelve Apostles. Immediately thereafter, he was set apart as Grant's First Counselor, with David O. McKay as the Second Counselor. Both positions became vacant upon the deaths of those who were previously serving. After President Grant's death, he was called as First Counselor to George Albert Smith. When George Albert Smith passed away, and David O. McKay became the President of the Church, J. Reuben Clark was called as President McKay's Second Counselor in the First Presidency. Clark was returned to the position of First Counselor after Stephen L. Richards' death in 1959 and continued to serve in that capacity until his own death on October 6, 1961.
As a member of the First Presidency, President Clark was a leading supporter of the Church welfare plan. He also helped put the finances of the Church on a budget plan. He was an inspirational leader and spoke forcefully on topics including freedom, his court, the inspired Constitutions, work, integrity, and chastity. An avid student of the life and teachings of the Lord Jesus Christ, he authored many scholarly books on gospel topics.
In addition to his Church duties, J. Reuben Clark continued to share his professional expertise as a member of corporate boards; government, political, and private committees; and academic journal and educational boards. He also bought and maintained a farm in Grantsville, his boyhood home.