Which country influenced the creation of communist governments in Eastern Europe after World War 2?

The Soviet Union.

The Soviet Union, under Joseph Stalin, considered itself to be the world's leader of Communism, since they had the world's first and only Communist country (which is a bit of a contradiction, but that's a story for another time).

As the Soviets liberated countries in Eastern Europe, they tended to work with local Communist parties in those countries, and then would install their leaders as the new rulers of the country. With a new Communist government in control, the Soviet Union would then control that government, and thus, that country.