Todor Hristov Zhivkov (Bulgarian: Тодор Христов Живков, tr. Todor Hristov Živkov; IPA: [ˈtɔdɔr ˈxristɔf ˈʒifkɔf]; 7 September 1911 – 5 August 1998), was the communist head of state of the People's Republic of Bulgaria (PRB) from March 4, 1954 until November 10, 1989.
He became First Secretary of the Bulgarian Communist Party in 1954 and remained on this position for 35 years, until 1989, thus becoming the longest-serving leader of any Eastern Bloc nation, and one of the longest ruling non-royal leaders in history.
More information on the English and Bulgarian Wikipedia pages.