German Chancellor Angela Merkel said on Monday she had the "greatest respect" for the German-born pope's "difficult" decision to step down due to his advanced age.
"He is and remains one of the most significant religious thinkers of our time," said Merkel, paying tribute to the pope.
"If the pope himself, after mature consideration, has come to the conclusion that he does not have the strength to carry out his office, that has my greatest respect," said Merkel, the daughter of a pastor.
"In this era of ever-increasing life expectancy, many people will understand how the pope had to battle with the burden of his age. Benedict XVI took his decision for his Church and the people within it," she added.
She paid tribute to his work in reaching out to other churches and other religions, including Jews and Muslims.
Merkel said the pope had "touched the heart of believers" on his trips to Germany and that his address to the Bundestag lower house of parliament was "still remembered."
"The words of the pope will stay with me personally for a long time," she said.
"As federal chancellor, I say thank you to Benedict XVI for his work and wish him all the best for the coming years."
Benedict XVI was born Joseph Ratzinger on April 16, 1927, in Marktl am Inn, in the predominantly Catholic southern German region of Bavaria.
He was ordained priest at the same time as his older brother Georg in 1951, and began teaching theology at Freising College in 1958.
Ratzinger went on from there to teach at several other German universities, notably in Bonn, Muenster and Regensburg.