"Today I wish to tell you that I have decided not to run again for the office of German president. The decision was not easy for me," Gauck said in Berlin. Speculation is already rife as to who might replace him.
Germany's 11th post-war president, Joachim Gauck, announced on Monday that he would not run for a second stint as head of state.
The 76-year-old said that he was worried about his ability to continue devoting enough energy to the job if he continued into his eighties.
"This decision was not easy for me," Gauck said at Bellevue Palace in Berlin. "I do not want to commit myself, for another period of five years, to levels of energy and vitality that I cannot guarantee."
Gauck said that he had served with "respect and joy" for more than four years, and that he was looking forward to the remainder of his term, which ends in February 2017.
German Justice Minister Heiko Maas said on Twitter that Gauck had "given dignity back" to the office of president thanks to his "high moral integrity." Maas also shared an old quote of Gauck's in his message: "People who say yes to their freedom, who doesn't just want it but also live it, to these people there flows a power that changes them, and this world."
The former pastor from then-communist East Germany said that the prospect of a change of president should not be a cause of concern, calling it "political normality" in a country with strong institutions and engaged voters.
General elections 2017 beckon
The timing for picking a replacement president could arguably be better. Gauck's successor will be chosen less than six months ahead of 2017's general elections, with the established parties struggling in the polls in recent regional votes.
Although the president in Germany is officially apolitical, it usually falls to Germany's parties to either agree on a unity candidate, or to field rival ones.
As Spiegel Online put it, Gauck's announcement effectively starts the general election campaign 15 months early, with a conflict Chancellor Angela Merkel would have preferred to avoid.
Green party co-chair Cem Özdemir hinted at this while honoring Gauck on Twitter shortly after the announcement: "Huge thanks and respect, President Gauck. We are happy that you remain our head of state until 2017. Now, please, no partisan tactics," Özdemir wrote.
Bavaria's state premier, Horst Seehofer, told reporters that his CSU conservatives would lobby for "a cross-party candidate standing for social justice and openness."
From Angela Merkel's CDU conservatives, Stanislaw Tillich, speaker of the upper house of parliament, said that Germany "needs another president with the ability to strengthen knowledge and understanding in society."
Several veteran political heavyweights have been linked with the soon-to-be-vacant post, including Christian Democrat (CDU) Finance Minister Wolfgang Schäuble, Social Democrat Foreign Minister Frank-Walter Steinmeier, speaker of the Bundestag parliament Norbert Lammert (also CDU), and Bavarian conservative Gerda Hasselfeldt.
"On speculation over the future president, I will say nothing and will not participate," Social Democrat chairman Sigmar Gabriel said. Asked about party colleague Steinmeier specificially, Gabriel said he was an excellent foreign minister, "who wishes to remain in the role, to the best of my knowledge."
A special congress of more than 1,000 people - many of them politicians but also including celebrities, sports stars and other public figures chosen by various political parties - elects Germany's president, over multiple votes if necessary.