Question

Which person fits the description. I began the Cold War in Europe by creating the Communist Bloc. I also stole atomic secrets for the United States and built my own bomb, thus escalating tension in the early Cold War.
Ronald Reagan
Dwight D. Eisenhower
Margaret Thatcher
Nikita Khrushchev
Harry S. Truman
Josef Stalin
Mikhail Gorbachev

Answer 1

The answer is Harry S. Truman

Answer 2

Correct answer:

Joseph Stalin

You may have meant "for," but then whoever wrote the question made a typo mistake in the question.  The only way the question makes sense is if it would read:  

• I began the Cold War in Europe by creating the Communist Bloc. I also stole atomic secrets from the United States and built my own bomb, thus escalating tension in the early Cold War.

The only possible answer is Josef Stalin.

Josef Stalin led the Soviet Union from the mid-1920s (after the death of Lenin) until 1953.

Under Stalin's leadership, the Soviet Union had conducted espionage concerning the United States "Manhattan Project," which was the US government's development of atomic bombs during World War II.  The US tested its first atomic bomb in July, 1945, and then used two such bombs to force Japan to surrender in August, 1945.

By 1949, the the Soviet Union had developed and tested its own atomic bomb.  From that point on, an arms race truly began between the two superpowers.