Benedict wrote three encyclicals, the most important form of papal document, including the 2007 "Spe Salvi" (Saved by Hope), an attack on atheism. The 2009 "Caritas in Veritate" (Charity in Truth) called for a rethink of the way the world economy is run.
Despite the difficulties that emerged from having two men wearing white in the Vatican, Francis developed a warm relationship with the man who was once nicknamed "the Panzer Cardinal" and said it was like having a grandfather in the house.
"He speaks little ... but with the same profundity as before," Francis once said.