This depends on the country or organization. See related questions or re-ask your question.
US: Harry S. Truman
Born May 8, 1884 in Lamar, Missouri, died December 26, 1972 in Kansas City, Missouri, Harry Truman succeeded Franklin D. Roosevelt as the thirty-third President of the United States, serving between April 12, 1945 and January 20, 1953, including the whole of 1951.
Harry S. Truman
Harry S. Truman was US president in 1951.
Dwight David Eisenhower served in 1959
Richard Nixon was vice-president from 1953 to 1961 including all of 1959.
January 3, 1959 the president was Dwight D. Eisenhower
The US president during WW2 was Franklin D. Roosevelt.
President - Charles de Gaulle, President of France (1959-1969)Prime Minister - Michel Debré, Prime Minister of France (1959-1962)
Abraham Lincoln was president during the US Civil War.
James Monroe, the 5th president of the US was president during the Missouri Compromise.
James Knox Polk was the US president during the Mexican War.
who was the us president at the time of the battle of France
Hawaii as the 50th US State in 1959 when Ike was the President.
The West German President during and after the building of the Berlin Wall was Theodore Heuss (1949-1959).
The Vietnam War was for 14 years (1959-1975), so there were more than one president during the war. The presidents were Dwight Eiesnhower, John Kennedy, Lyndon Johnson and Richard Nixon and Gerlad Ford.