Imprisoned from 1953 to 1956, Karmal befriended fellow inmate Mir Akbar Khyber, who introduced Karmal to Marxism. Karmal changed his name from Sultan Hussein to Babrak Karmal, which means "Comrade of the Workers'" in Pashtun, to disassociate himself from his bourgeois background. When he was released from prison, he continued his activities in the student union, and began to promote Marxism. Karmal spent the rest of the 1950s and the early 1960s becoming involved with Marxist organizations, of which there were at least four in Afghanistan at the time; two of the four were established by Karmal. When the 1964 Afghan Provisional Constitution, which legalised the establishment of new political entities, was introduced several prominent Marxists agreed to establish a communist political party. The People's Democratic Party of Afghanistan (PDPA, the Communist Party) was established in January 1965 in Nur Muhammad Taraki's home. Factionalism within the PDPA quickly became a problem; the party split into the Khalq led by Taraki alongside Hafizullah Amin, and the Parcham led by Karmal.