Short answers, pulled from the story.
James F. Byrnes was a South Carolina politician who served in the U.S. House, the U.S. Senate, the Supreme Court, and as the 49th U.S. Secretary of State under President Harry S. Truman, as well as the 104th governor of South Carolina. Historian George E. Mowry called him "the most influential Southern member of Congress between John Calhoun and Lyndon Johnson."
Byrnes served on the Supreme Court from the 8th of July, 1941, until the 3rd of October, 1942, a tenure of just 15 months. President Roosevelt asked him to leave the Court after America's entry into World War II to lead the Office of Economic Stabilization and later the Office of War Mobilization, making his tenure the shortest of any justice in history.
Byrnes headed the Office of Economic Stabilization beginning in 1942 and became head of the Office of War Mobilization in May 1943. Known in Washington as the "Assistant President," he managed factories, civilian and military production, and transportation for U.S. Armed Forces personnel, and provided oversight for the Manhattan Project. He also served on the Interim Committee that made recommendations on the use of the atomic bomb.
Byrnes delivered the "Restatement of Policy on Germany," also known as the "Speech of Hope," in Stuttgart, Germany on the 6th of September, 1946. Heavily influenced by General Lucius D. Clay, the speech formally repudiated the Morgenthau Plan, which would have permanently deindustrialized Germany, and marked the transition of American policy toward economic reconstruction of postwar Germany.
Relations between Byrnes and President Truman deteriorated after Truman believed Byrnes was setting foreign policy independently and informing the President only afterward. Truman was also dissatisfied with Byrnes's conciliatory approach toward the Soviet Union, particularly after the Moscow Conference in December 1945. Byrnes resigned from the Cabinet in January 1947 with feelings of bitterness.
As governor of South Carolina, Byrnes asked Kansas to submit an amicus curiae brief defending a state's right to segregate its schools in the NAACP's lawsuit against South Carolina. That request gave NAACP lawyer Thurgood Marshall the idea to shift the suit from South Carolina to Kansas, which led directly to the Supreme Court case Brown v. Board of Education.