Benedict XVI says he is stepping down at the end of the month, lacking the strength to fulfill his duties at the head of the Catholic Church. The 85-year-old German becomes the first pontiff to resign in nearly 600 years. Here are some key events in the life of a conservative pontiff who grappled with a global sex abuse scandal that exploded during his leadership:
— April 16, 1927: Born Joseph Alois Ratzinger in Marktl am Inn, Germany, youngest of three children to Joseph and Maria Ratzinger.
— 1943-1945: Assistant in Germany's anti-aircraft defense and infantry soldier; imprisoned in 1945 in American POW camp in Neu-Ulm.
— June 29, 1951: Ordained along with brother Georg Ratzinger in Freising.
— 1969-1977: Professor at University of Regensburg.
— March 25, 1977: Named archbishop of Munich and Freising.
— June 27, 1977: Made a cardinal by Pope Paul VI.
— Nov. 25, 1981: Named prefect of the Congregation for the Doctrine of the Faith by Pope John Paul II; takes up post in March 1982.
— April 2, 2005: Pope John Paul II dies.
— April 8, 2005: As dean of the College of Cardinals, Ratzinger presides over John Paul's funeral.
— April 19, 2005: Elected 265th pope in one of the fastest conclaves in history. Choosing name Benedict XVI, he says he is merely a "simple, humble worker in the vineyard of the Lord."
— April 24, 2005: Installed as pope with Mass.
— Aug. 18-21, 2005: First foreign trip, to World Youth Day in Cologne, Germany.
— Sept. 24, 2005: Meets with dissident theologian Hans Kung at papal summer residence.
— Dec. 25, 2005: First encyclical "God is Love" signed. Released Jan. 25, 2006.
— May 28, 2006: During trip to Poland, visits Auschwitz concentration camp.
— Sept. 12, 2006: During visit to Germany, delivers speech at University of Regensburg that enrages Muslims; quoting a Byzantine emperor who characterized some of the teachings of the Prophet Muhammad as "evil and inhuman," particularly "his command to spread by the sword the faith."
— April 16, 2007: First volume of "Jesus of Nazareth" completed on his 80th birthday. Released April 13.
— May 27, 2007: Signs letter to China's Catholics, urging them to unite under his authority. Published June 30.
— July 7, 2007: Removes restrictions on celebrating the old Latin Mass in major gesture to traditional Catholics.
— April 20, 2008: During visit to United States, prays for victims of Sept. 11, 2001 attacks at ground zero.
— July 19, 2008: During visit to Australia for World Youth Day, meets with victims of priestly sex abuse and during a Mass apologizes for their suffering.
— Jan. 21, 2009: Lifts excommunication of Holocaust-denying Bishop Richard Williamson and three other ultra-traditionalist bishops of Society of St. Pius X, igniting outrage. Decree released Jan. 24.
— March 10, 2009: Acknowledges Vatican mistakes in Williamson affair, says Vatican must make better use of Internet to prevent future controversies. Letter released March 12.
— March 17, 2009: En route to Cameroon, tells reporters aboard papal plane that condoms are not the solution to AIDS and can make problem worse, prompting widespread criticism.
— May 11, 2009: During visit to the Holy Land, lays wreath at Yad Vashem memorial in Jerusalem, says Holocaust victims "lost their lives but they will never lose their names."
— June 29, 2009: Third encyclical "Charity in Truth" signed. Released July 7, 2009.
— July 17, 2009: Breaks right wrist in late-night fall at summer vacation home.
— Oct. 20, 2009: Vatican announces pope is making it easier for Anglicans to convert en masse to Catholicism.
— March 19, 2010: Rebukes Irish bishops for "grave errors of judgment" in handling clerical sex abuse but makes no mention of Vatican responsibility in letter to Irish faithful. Released March 20.
— May 1, 2010: Orders major overhaul of Legion of Christ after Vatican investigation determines founder was a fraud.
— Sept. 16-19, 2010: During first state visit by a pope to Britain, meets with Queen Elizabeth II, Archbishop of Canterbury Rowan Williams and beatifies Anglican convert John Henry Newman.
— Nov. 20, 2010: Revises controversial condom-AIDS comments in book and says male prostitutes who use condoms may be taking a first step toward a more responsible sexuality.
— March 2, 2011: Issues sweeping exoneration of Jews for the death of Christ in "Jesus of Nazareth-Part II." Book released March 10.
— May 1, 2011: Beatifies John Paul II before 1.5 million people.
— June 28, 2011: Tweets for the first time, announcing launch of Vatican news information portal.
—Oct. 6, 2012 — Pope's former butler is convicted on charges he stole the pontiff's private letters and leaked them to a journalist.
— Feb. 11, 2013: Reveals in Latin that he is stepping down Feb. 28 during a meeting of Vatican cardinals, surprising even his closest collaborators.