Koltsov was the son of a Jewish shoemaker and the brother of Boris Efimov. Koltsov participated in the Russian Revolution of 1917, became a member of the Bolshevik party in 1918, and took part in the civil war. A convinced communist, he soon became a key figure of the Soviet intellectual elite and arguably the most famous journalist in the USSR, chiefly due to his well-written satirical essays and articles, where he criticised bureaucracy and other negative phenomena in the Soviet Union. Koltsov founded popular journals such as Krokodil, Chudak and Ogonyok and was a member of the editorial board of Pravda. As a Pravda correspondent, he travelled to Spain to cover the Spanish Civil War, while at the same time he was working for the NKVD. He also acted as military advisor to Loyalist forces