Who started the Cold War?
There are many different answers to this question, but in my opinion, the person that really made start the Cold War was Stalin, the dictator of the Soviet Union.
During the Yalta conference, that was organized by the countries that won the war in february 1945 (Britain, USA, USSR), Stalin garanteed to the leaders of those nations that he wanted free democratic election in the whole Eastern Europe. But in reality he had a completely different plan in his mind: his thirst of power, and his expansionist aims, act to procure supplies
to the nation that was in the middle of a giant crisis due to the war, brought him to inglobate in the already giant "Soviet sphere" the countries that he promised to make become democratic.
Furthermore, Stalin in 1946 said: "Capitalism and Communism cannot cohesist", which, indirectly, is a declaration of an imminent war. In this way he sent a strong and clear message to the whole world saying that from there on, it would have been divided in two by an imaginary line, called Iron Curtain, that passed through Stettin, in the very North of Europe, and Trieste, a small city in the Eastern of Europe. This curtain locked down the Soviet Union and all her satellites, so that the nobody could have seen what was happening inside the borders of the Communist countries.
Moreover, when USA, Britain and France wanted to make the Western Germany a democratic country with capital Berlin, he opposed with all his strength, declaring the blockade of all the streets and electricity and water conducts that arrived in the Western part of Berlin, forcing USA, Britain and France to use airlift to bring supplies in the city.