But when the German cardinal began his papacy yesterday with the words "I accept," Ratzinger moved into a role embodying attitudes and ideology he has helped to mold for nearly 25 years, as the top theological adviser to his predecessor, Pope John Paul II.
His positions against contraception and women in the clergy are the worldwide teachings of the church, and his status as a leader in the Vatican was established well before he donned his white cassock.
"He's a true intellectual whose mark on the church is already apparent, and will only grow now," said Lawrence S. Cunningham, a professor of theology at the University of Notre Dame. "What he is not is the gregarious, media-savvy individual you might have expected. I find it hard to imagine him clapping and swaying at World Youth Day."
From his conscription into the Hitler Youth and the German army during World War II to his strong-armed enforcement of traditional doctrine under Pope John Paul, the life of Ratzinger has earned him a reputation as a hardened student of world events and witness to the church's evolution. He is a theological conservative - almost legendarily so - but is also one of Catholicism's more notable writers and thinkers.
Ratzinger participated in the church's reformation during the Second Vatican Council of the 1960s, then steered it back toward its old traditions as a top aide to Pope John Paul and one of the few cardinals granted regular, private audiences with him.
His commitment to the conservative ideals that he and his predecessor espoused earned him unflattering nicknames such as Der Panzerkardinal, or the Grand Inquisitor. But Catholic scholars say none of those characterizations truly captures the complexity of the man whom noted Catholic author Andrew M. Greeley called "perhaps the most important theologian of the 20th century."
"You can't have the job as the enforcer for orthodoxy and not appear to be the heavy - the bad guy," said the Rev. Jim Heft, chancellor of the University of Dayton and a professor of faith and culture. "But he is also a first-rate theologian."
"It's a great theological sport for those of us in the academy to compare 'modern Ratzinger' with 'early Ratzinger,'" said Cunningham. "That speaks to his increasing conservatism over the years, but also to his considerable contribution to Catholic study and thought."
Ratzinger was born in the Bavarian town of Marktl Am Inn but moved often to accommodate his father's job as a rural police officer. He recalls in his memoirs how his family watched the Nazi party strengthen its hold on Germany, once forcing them to move to escape party followers. He recounts a teacher who tried to supplant traditional Catholic ceremonies with a Maypole ceremony, calling it more fitting of Germanic ways.
Ratzinger and his brother, Georg, joined the Hitler Youth in 1941 when it became compulsory, but he was soon released to join the priesthood. He was later drafted into the German army and assigned to an anti-aircraft brigade defending a BMW plant outside Munich, where he says he never fired a weapon.
The young seminarian risked his life by deserting in 1945 and was captured by U.S. soldiers and sent to a prisoner of war camp for the rest of the war. In Milestones: Memoirs 1927-1977, Ratzinger recalls the terror of being confronted by German soldiers after his desertion.
"Thank God they were ones who had had enough of war and did not want to become murderers," he wrote. "They had to find a reason to let me go. I had my arm in a sling [from] an injury."
"Comrade, you are wounded," they told him. "Go on."
Ratzinger's experience in Nazi Germany is thought to have been a seminal moment in the formation of his theological convictions, convincing him that church teachings must be clear and absolute lest they be easily manipulated by outside forces.
"Having seen fascism in action, Ratzinger today believes that the best antidote to political totalitarianism is ecclesial totalitarianism," wrote John L. Allen Jr., in his book Cardinal Ratzinger: The Vatican's Enforcer of the Faith. "In other words, he believes the Catholic church serves the cause of human freedom by restricting freedom in its internal life, thereby remaining clear about what it teaches and believes."
Another formative period of his theological life came in the late 1960s, when the voice of political radicalism that challenged institutions in Germany caused him to withdraw into the relative safety and security of church doctrine. "He was traumatized by the protests of the 1960s, and his conservatism basically solidified," said Cunningham.
Ratzinger was a professor of theology at universities in Germany in the 1960s and was appointed Archbishop of Munich in 1977. Pope John Paul called him to the Vatican in 1981 to become prefect of the Congregation for the Doctrine of the Faith, the lead enforcer of church's teachings.
Though he has lived in Italy for 24 years and speaks numerous languages in addition to his native German - including fluent English and Italian - he is, by all accounts, a proud native of his homeland. Biographer Allen wrote: "Almost as much as John Paul II is Polish, Joseph Ratzinger is Bavarian."
In selecting the name Benedict, Ratzinger chose to follow Pope Benedict XV , a World War I-era pope who is remembered for his efforts to broker peace. Perhaps more fitting, observers say, he assumes the name of Saint Benedict of Nursia, the patron saint of Europe.
A homily that Ratzinger delivered Monday, which railed against a "dictatorship of relativism" threatening to dilute church doctrine, was widely seen as a rebuke of church leadership in Europe, where Vatican officials fear that a secular movement is undermining their authority and their message.
As the first German pope in nearly a millennium, Ratzinger could help energize one of the church's flagging constituencies.
His time could be limited, but the aged pontiff will likely recall the tenure of Italian Cardinal Angelo Roncalli, who became Pope John XXIII at age 77, a year younger than Ratzinger. Pope for five years, he sparked a revolution in the church by calling the Second Vatican Council, which reopened church law and did away with such traditions as Mass spoken only in Latin.
"John XXIII blew the lid off the church, and he was supposed to be a transitional pope," said Heft. "What's going to be interesting now is to see whether there is a side to Joseph Ratzinger that we haven't seen before. I think if he wanted simply to follow in the steps of John Paul he would have called himself John Paul III, but he didn't. We're going to see something different."