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. Continued...