Yes, the answer is definitely Joseph Stalin. He led the USSR from 1928 until he died in 1953.
Of the other people in your choices, Winston Churchill was the leader of Great Britain, not of the USSR. Harry Truman was the President of the United States for the last few months of the war. Anastasio Somoza was a dicator in Nicaragua. Adolph Hitler ruled Germany. Dwight Eisenhower and Douglas MacArthur were generals in the United States Army. Eisenhower was the commander in charge of all Allied forces in Europe -- he led the D-Day landings. MacArthur was the head of all Allied forces in one part of the Pacific and is famous as the man in charge of the push towards Japan.