Patriarch Maxim, a conservative who led Bulgaria's Orthodox Church for 41 years in times of Communist rule and democracy, died at age 98, the church said on Tuesday.
"This night, about at 4 a.m., at the age of 98 the head of the Bulgarian Orthodox Church, his Holiness Bulgarian Patriarch and Bishop of Sofia Maxim presented himself to God," the statement said.
The patriarch had been in hospital in the past weeks, suffering a general weakness, doctors have said.
Since 1971, Maxim has been a patriarch of Bulgaria's 1,100-year-old Orthodox Church, which survived centuries of Turkish domination and decades of atheistic communism.
Under Bulgarian Orthodox Church procedures, a Holy Synod of 13 senior clergy will meet to make funeral arrangements and choose an interim patriarch until a larger Church Council is held within the next four months to pick Maxim's successor.
About 80 percent of Bulgarians say they are Eastern Orthodox Christians.
Patriarch Maxim has kept a low public profile but was an influential figure with a controversial past.
He oversaw a major religious revival in Bulgaria after the collapse of the communist rule. Dozens of new churches were built across the country and monasteries reopened.
He was elected Patriarch in 1971 during Communist rule, which did not outright ban religious practices, but scorned those who attended mass and deprived them of career development.
After the fall of communism in 1989, rebel clerics split from the Holy Synod, setting up an alternative Orthodox Church, accusing Maxim of collaborating with the former repressive regime and questioning the legitimacy of his election.
The rebels said Maxim was not rightfully elected but named by late communist dictator Todor Zhivkov.
Maxim consolidated support and managed to keep his post. After years of bitter schism and separation, the church united in 1998, with the last rebel priests repenting 10 years later.
A recent report from a history commission established that there were no documents linking Maxim with much feared secret police, but found that 11 out of the Balkan country's 15 bishops had been collaborators to the communist regime.
Maxim was born as Marin Naidenov Minkov on Oct. 29, 1914 in the central Bulgarian village of Oreshak. Maxim took Holy Orders in 1941 and became secretary general of the Holy Synod in 1955.