Whatever his past, few expected Benedict to announce he was stepping down, including world and Catholic leaders, who voiced admiration for his decision and the man himself.

U.S. Vice President Joe Biden, himself a Catholic, said he thought the pope set "an incredibly high standard" by understanding his own limitations and how they might affect the church.

"The decision reinforces for me as a practicing Catholic that this is a man of great integrity and looking out for what he believes is in the best interest of our church," Biden said. "I admire him for it."

British Prime Minister David Cameron said Benedict "will be missed as a spiritual leader to millions." Cameron's Irish counterpart, Enda Kenny, praised Benedict for decades of leadership and service, as well as his decision to resign.

"It reflects his profound sense of duty to the Church, and also his deep appreciation of the unique pressures of spiritual leadership in the modern world," Kenny said in a prepared statement.

Archbishop Vincent Nichols, the president of the Catholic Bishops' Conference of England and Wales, said the decision "shocked and surprised everyone."

"Yet, on reflection, I am sure that many will recognize it to be a decision of great courage and characteristic clarity of mind and action," he said.

Archbishop Timothy Dolan, president of the U.S. Conference of Bishops, said he was startled, and sad, to see Benedict resign.

"It's like watching your own Dad get old and admit he's not up to all the duties that being the head of a family involves," Dolan said. "And there's a somberness, there's a sadness there."