The former Cardinal Joseph Ratzinger was head of the Congregation for the Doctrine of the Faith - once known as the Holy Office of the Inquisition - from 1981 until his election.
His defence of church doctrine led to him be called "the Pope's enforcer" and "God's rottweiler".
Since his election, the Vatican has been at pains to portray a softer image.
The music-loving, professorial Pope is described by those who know him as laid back, with a mild and humble manner.
Pope Benedict has a lower profile than that of his predecessor, John Paul II, and lacks his charisma and showmanship.
Despite this apparent lack of populist appeal, Pope Benedict consistently draws crowds as large as those of the late John Paul II to his weekly audiences.
Joseph Ratzinger was elected to the papacy in April 2005. At the age of 78, he was the oldest cardinal to become Pope since Clement XII was elected in 1730.
The public image was of a staunch defender of conservative theology. He campaigned against liberation theology, which had gained ground among priests in Latin America and elsewhere as a means of involving the Church in social activism and human rights issues - but to him it was too close to Marxism.
Joseph Ratzinger was born into a traditional Bavarian farming family in 1927, although his father was a policeman.
The eighth German to become Pope, he speaks many languages and is said to be an accomplished pianist with a preference for Beethoven.
At the age of 14, he joined the Hitler Youth, as was required of young Germans of the time, but was not an enthusiastic member.
His studies at Traunstein seminary were interrupted during World War II when he was drafted into an anti-aircraft unit in Munich.
He deserted the German army towards the end of the war and was briefly held as a prisoner of war by the Allies in 1945.
His supporters say his experiences under the Nazi regime convinced him that the Church had to stand up for truth and freedom.
The Pope's conservative, traditionalist views were intensified by his experiences during the liberal 1960s.
He taught at the University of Bonn from 1959, and in 1966 took a chair in dogmatic theology at the University of Tuebingen.
However, he was appalled at the prevalence of Marxism among his students.
One incident in particular at Tuebingen, in which student protesters disrupted one of his lectures, seems to have particularly upset him.
In his view, religion was being subordinated to a political ideology that he considered "tyrannical, brutal and cruel".
"That experience made it clear to me that the abuse of faith had to be resisted precisely," he later wrote.
In 1969 he moved to Regensburg University in his native Bavaria - where he would return as Pope to make his controversial remarks on Islam in September 2006 - and eventually rose to become its dean and vice-president.
He was named Cardinal of Munich by Pope Paul VI in 1977.
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