What did Joseph Stalin do in the Cold War?

Joseph Stalin was one of the most important figures in the
entire Cold War.  You could say that he was the cause of the Cold War.  Whether he was
the cause or not, he was certainly one of the most important actors in the beginning of
the Cold War.

Stalin was the leader of the Soviet Union
from the 1920s until his death in 1953.  This means that he was the center of power in
the USSR during the years in which the Cold War was beginning.  His attitudes towards
the West and towards Eastern Europe helped to bring about the Cold
War.

Stalin wanted to have a large buffer zone of Eastern
European countries to be under his control.  He wanted them to protect the Soviet Union
from invasion from the West.  Because of this, he was determined to keep control of
Eastern Europe after WWII.  His determination to dominate Eastern Europe helped to scare
the West and push it to take a more aggressive anti-communist line.  Stalin’s actions,
such as the blockade of West Berlin, helped to solidify the antagonism between the two
sides.

Thus, what Stalin did in the Cold War was to help
create the atmosphere of mutual animosity that drove that
conflict.