It depends on when you think the Cold War started. If you argue that the origins of the Cold War go back to the Bolshevik Revolution, then the responsible party for starting the Cold War would be the United States, because the United States sent 13,000 troops (known as the American North Russian Expeditionary Force or by its nickname, the Polar Bear Expedition) to the Russian cities of Archangel and Vladivostok in 1918 as part of an Allied force to overthrow the new Bolshevik government. Most American history students don't know this fact until they're in college or grad school (if ever), but Soviet kids would learn this in grade school.
