Komitat Hont
Gerő was born in Terbegec, Hont County of the Kingdom of Hungary (now Trebušovce, Slovakia) to Jewish parents, although he later totally repudiated religion. An early Hungarian communist, Gerő fled Hungary for the Soviet Union after Béla Kun's brief Soviet government was overthrown in August 1919. During his two decades living in the USSR, Gerő was an active NKVD agent. Through that association, Gerő was involved in the Comintern—the international organization of communists—in France, and also fought in the Spanish Civil War, during which he performed purges against Trotskyist groups in the International Brigades. As a result he was called the "Butcher of Barcelona".