Answer: Directly, The National Liberation Front, or the EAM/ELAS (A Communist Insurgency in Greece).
Indirectly, Communists in general.
Explanation:
The world in 1947 was a very different one from the world in 1945 for whereas in the former the West and ghe Soviet Union had been triumphant Allies who vanquished the Nazis in the Second World War, in the latter they were rivals, competing to impose their own view of Political theory on the world.
The British had been responsible for liberating Greece in the Second World War which is why it had not fallen into the hands of the Soviets and Turkey had maintained neutrality, only joining the War in the last months and never actually fighting so they didn't fall into the hands of the Soviets either.
Britain supplied Aid to both countries to keep them from falling into Soviet Communism but in 1947 could do no more because the British Economy had barely survived the war.
They informed the USA and after some negotiations with Congress, President Truman uttered the very popular, Truman Doctrine.
In his speech he said, "It must be the policy of the United States to support free peoples who are resisting attempted subjugation by armed minorities or by outside pressures."
The armed minority he was directly referring to were the National Liberation Front, or the EAM/ELAS which was waging an insurgency in Greece at the time but in general, he wanted the United States to take a stand against all communists groups that would attempt to take over nations by force and against the Soviet Union that would attempt to place pressure on countries to join their side.
