Pope Benedict XVI announced today that he will resign Feb. 28, saying his role requires "both strength of mind and body."
The pope's decision makes him the first pontiff to resign in nearly 600 years. A conclave to elect a new pope will take place before the end of March. The 85-year-old pope announced the decision to resign in Latin during a meeting of Vatican cardinals.
"After having repeatedly examined my conscience before God, I have come to the certainty that my strengths due to an advanced age are no longer suited to an adequate exercise of the Petrine ministry," he said. "I am well aware that this ministry, due to its essential spiritual nature, must be carried out not only by words and deeds but no less with prayer and suffering."
Pope Benedict XVI was the oldest pope to be elected at age 78 on April 19, 2005. He was the first German pope since the 11th century and his reign will rank as one of the shortest in history at seven years, 10 months and three days.
The last pope to resign was Pope Gregory XII, who stepped down in 1415.
Vatican officials said they've noticed that he has been getting weaker, while Benedict said he is aware of the significance of his decision and made it freely.
Vatican Communications Director Greg Burke told ABC News that he was surprised but not shocked by the announcement, and cited an interview in which Benedict said a pope not only could resign, but should resign, if necessary.
"[Pope Benedict] is slowing a bit, and there's nothing immediately serious or grave," Burke said. "He has an older brother. He just thought the demands of the job were too much for his physical well being."
Benedict's brother, Monsignor Georg Ratzinger, had shared his concerns about the pope's health in September 2011, telling Germany's Bunte magazine that he should resign if health issues made the work impossible. More recently, Ratzinger has apparently cited his brother's difficulty in walking and his age, saying that Benedict had been advised by his doctor to cease transatlantic trips and that he had been considering stepping down for months, according to the German DPA news agency.
Among other ailments, the pope reportedly suffers from arthritis and arthrosis -- a debilitating joint-degeneration condition -- and his declining health drew attention about a year ago when he used a cane at the airport on his way to a trip to Mexico and Cuba.
Benedict has been a less charismatic leader than his predecessor, John Paul II, but tending to the world's roughly 1 billion Catholics still requires stamina Benedict seems to believe he now lacks.
"Obviously, it's a great surprise for the whole church, for everyone in the Vatican and I think for the whole Catholic world," the Rev. John Wauck, a U.S. priest of the Opus Dei, told "Good Morning America" today. "But, at the same time, it's not completely surprising given what the pope had already written about the possibility of resigning.
"It's clear in terms of his mental capacity he's in excellent shape, he's very sharp, and so when he says he's making this official with whole freedom, it's clear that that's the case, that makes one believe that this is an act taken out of a sense of responsibility and love for the church."
It is a road that leads back to the 1930s.
Ratzinger started seminary studies in 1939 at the age of 12. In his memoirs, he wrote of being enrolled in Hitler's Nazi youth movement against his will when he was 14 in 1941, when membership was compulsory. In 1943, he was drafted into a Nazi anti-aircraft unit in Munich. He says he was soon let out because he was a priest in training.
He returned home only to find an army draft notice waiting for him in the fall of 1944.
As World War II came to an end, the 18-year-old Ratzinger deserted the army. In May 1945, U.S. troops arrived in his town and he was sent to a prisoner-of-war camp.
In his memoir, he says that he became convinced God "wanted something from me, something which could only be accomplished by becoming a priest."
"I was shy and unpractical, had no talent for sports or organization or administration," he wrote. "I had to ask myself if I would ever be able to connect with people."
Ratzinger later recalled that during this dark time the church served as "a citadel of truth and righteousness against the realm of atheism and deceit."
After the war, Ratzinger returned to the seminary where he was known to play Mozart on the piano. He and his older brother, Georg, were ordained priests June 29, 1951. Three years later, he received his doctorate in theology from the University of Munich and began teaching in Bonn, the first of several appointments in German universities.
Chosen as an adviser to the Second Vatican Council in 1962, when the church became more open under Pope John XXIII, Ratzinger was a progressive voice in updating church laws on heresy.
Hans Kung, the Swiss theologian, was so impressed by Ratzinger's intellect that in 1966 he brought him on as staff at the University of Tubingen, without interviewing other candidates, a practice unheard of in German universities.
But the radicalism he encountered there bothered him. He opposed the 1968 Marxist student demonstrations and left the university for his native Bavaria to teach at a more conservative university.
"I had the feeling that to be faithful to my faith I must also be in opposition to interpretations of the faith that are not interpretations but oppositions," he later said.
It was during the 1970s that Ratzinger explored his deepest theological thoughts.
In 1977, Ratzinger was appointed bishop of Munich and elevated to cardinal three months later by Pope Paul VI. He was one of only two cardinals in the latest conclave who were not chosen by John Paul II.
That same year he was appointed to the Synod of Bishops, an advisory council to the pope, and met the archbishop of Krakow, Karol Cardinal Wojtyla, the future Pope John Paul II.
They found they were both intellectual, multilingual church men despite their different styles: a soft-spoken, polite Bavarian vs. the athletic, media loving anti-Communist Pole.
When Wojtyla was elected pope in 1978, he invited Ratzinger to Rome.
After overcoming Ratzinger's objections, John Paul named him to head the Congregation for the Doctrine of the Faith as guardian of church dogma.
A Vatican spokesman acknowledged that some papal appointments were influenced by politics but Ratzinger was "one of the most personal choices" of John Paul's pontificate.
Ratzinger later became the Vatican official responsible for reigning in dissident clergymen like his old mentor Kung, whose license to teach theology was revoked by the Vatican in 1979.
He explained that during Vatican II he began to have second thoughts about the new direction the clergy was taking.
"I found the mood in the church and among theologians to be agitated," he wrote. "More and more there was the impression that nothing stood fast in the church, that everything was up for revision."
A conservative on issues such as homosexuality and the ordination of women, Benedict also denounced rock music, dismissed anyone who tried to find "feminist" meanings in the Bible, and denied Communion to those who supported abortion and euthanasia.
As his stances hardened, the nicknames piled on from "God's Rottweiler," to "the German Shepherd" to "Cardinal No."
As John Paul II's health declined, Ratzinger took over more and more responsibility at the Vatican. In 2002, he became dean of the College of Cardinals, which didn't seem to slow down his prolific writing.
The pontiff authored more than 30 titles including: "Pilgrim Fellowship of Faith: The Church as Communion," "Truth and Tolerance: Christian Belief and World Religion," "The Spirit of the Liturgy" and "Milestones: Memoirs 1927-1977."
In the days after Pope John Paul II's death April 2, 2005, the shy and humble Ratzinger stepped into the spotlight. He delivered a heartfelt homily at John Paul's funeral followed by a fiery speech to the cardinals.
Before the cardinals started the secret process of choosing a successor, he warned them about tendencies that he considered dangers to the faith: sects, ideologies like Marxism, liberalism, atheism, agnosticism and relativism -- the ideology that there are no absolute truths.
"Having a clear faith, based on the creed of the church is often labeled today as a fundamentalism," he said. "Whereas relativism, which is letting oneself be tossed and swept along by every wind of teaching, looks like the only attitude acceptable to today's standards."
Despite thoughts that his conservative penchant would keep him out of the running, Ratzinger's election to St. Peter's throne was swift.
His election in four ballots in two days was one of the shortest in 100 years. He is also the oldest pope elected since Clement XII in 1730.
If Ratzinger was paying tribute to the last pontiff named Benedict, it could be interpreted as a bid to soften his image as "God's Rottweiler." Benedict XV reigned during World War I and was credited with settling animosity between traditionalists and modernists, and dreamed of reunion with Orthodox Christians.
The name he took draws a connection to Benedict XV, the Italian pontiff from 1914 to 1922 who had the difficult task of providing leadership for Catholic countries on opposite sides of World War I. His declared neutrality and humanitarianism was demonstrated in his untiring efforts to relieve the sufferings of the war.
He founded a bureau for the exchange of wounded prisoners and a missing-persons bureau and established relief agencies.
Benedict was also known for his outreach to Muslims and efforts to close the nearly 1,000-year estrangement with Christian Orthodox churches.
Taking on the Papal Role
In his homily after assuming the role of pope, Pope Benedict XVI told the faithful, "The Church is young." As a cardinal known for his strict orthodoxy, Benedict struck a softer note. He said he did not need to lay out a governing program.
Immediately after the Mass, a white Jeep pulled up to the steps of the basilica, and Pope Benedict XVI climbed in. There was no bulletproof glass as he drove around for what was described as a victory lap.
In his first weeks as Pope, Benedict pledged to work for reconciliation and peace among peoples.
He also referred to the Christian roots of Europe, in what was a major theme of his papacy.
He was also forced to address accusations that priests had sexually abused boys.
As the Catholic church was rattled in 2005 by such allegations, the Vatican published "Criteria for the Discernment of Vocation for Persons with Homosexual Tendencies."
It was widely viewed as the church's response to the worldwide scandal, but was also criticized for drawing a connection between pedophilia and homosexuality.
In 2008, the pope said the clergy sex abuse scandal in the United States made him feel "deeply ashamed." In 2010, Benedict apologized directly to victims and their families in Ireland.
"You have suffered grievously and I am truly sorry," he wrote to victims of child sex abuse by clergy in Ireland.
In his only visit to the United States as pope, Benedict was welcomed for an elaborate state visit arrival at the White House in 2008. President Obama was granted an audience at the Vatican just months after taking office, although the Obama administration and the church have clashed on important issues, including abortion, contraceptive services, and stem cell research.