This article was updated February 11, 2013.
For the first time in more than 500, years a sitting Pope resigned today. Benedict cited deteriorating strength and "advanced age," shocking Vatican-watchers and Catholics around the globe. (Notably, he didn't announce the news on Twitter, even though he's a user. Instead he used Latin, and half the Cardinals in attendance had no idea what he said.)
It's been a controversial eight years: Having thoroughly offended Muslims, and seen his secretary tried for leaking secrets, overshadowing even these lapses has been the global sex abuse scandal. Pope Benedict also offended many with his most recent book, "Jesus of Nazareth: The Infancy Narratives" caused a huge controversy by questioning a number of long-held beliefs about the Christmas story (what, no animals in the stable?). Now that he's retired, might we expect more books from him? If so, they join these definitive books by he and his predecessors that delve into what it's like to hold the highest Catholic office the world around.
Pope Paul VI
The Pope who presided over the Second Vatican Council, Paul VI, is called by many the first "modern pope." The former Giovanni Battista Enrico Antonio Maria Montini was perhaps most famous for his "Humanae Vitae," an encyclical letter published in 1968 that reaffirmed the church's traditional teachings on marriage, love, sex and procreation. For more on the man, "Christian Values and Virtues," a posthumously-published collection of his teachings, lays bare both his doctrinal positions and his views on how modernity could square with the teachings of the Catholic Church.
John Paul II
Karol Wojtyła, who in 1978 became Pope John Paul II, was one of the most charismatic modern-day popes. Beloved by his flock--perhaps more beloved than almost all other popes in recent memory--Polish John Paul II charmed with the warmth of his personality, and his approachability: His international bestseller, "Crossing the Threshold of Hope," revealed a fine sense of humor as much as it drove home a central teaching, which is to "be not afraid" (a moving statement, considering that around half-way through his papacy he witnessed--some say, partly helped herald--his former homeland's liberation from Communist rule).
Joseph Aloisius Ratzinger's ascent to the head of the Catholic Church came not via his force of personality, as Karol Wojtyła's did before him. Instead, Ratzinger became Pope Benedict XVI through this Vatican insidership--he headed the powerful Congregation for the Doctrine of the Faith, an organization within Rome that helps set straight Catholic theology. An unabashed intellectual, Benedict XVI has used books as one of his main tools to reach the faithful in more approachable ways. Not only did his most recent book cause a Christmas controversy, but in the first book he published as Pope, "Jesus of Nazareth: From the Baptism in the Jordan to the Transfiguration," he shows that a close engagement with the facts of Jesus' life, rather than merely with dry doctrine, will lead to a deeper faith and a happier world.