BERLIN — Horst Kohler, a onetime head of the International Monetary Fund who became a popular German president before stunning the country by resigning abruptly in a flap over comments about the country’s military, has died. He was 81.

Kohler, who was head of state from 2004 to 2010, died Saturday morning in Berlin after a short illness, surrounded by his family, the office of current German President Frank-Walter Steinmeier said in a statement.

Kohler was little known to most Germans and a stranger to front-line politics before he won the presidency. His nomination was greeted by the mass-

circulation daily Bild with the headline “Horst Who?”

However, he built up high popularity ratings once in the job, something that he achieved in part by positioning himself as an outsider to the country’s political elite.

He occasionally refused to sign bills into law due to constitutional concerns and didn’t always make himself popular with the government of Chancellor Angela Merkel, whose choice he was for the presidency — a largely ceremonial job but often seen as a source of moral authority.

Kohler was elected before Merkel came to power, at a time when Germany was struggling to come to terms with labor market reforms and welfare state cuts. He said Germans must not rest on past achievements, and said he was “deeply convinced Germany has the strength for change.”

In July 2005, Kohler agreed to dissolve parliament and grant struggling then-Chancellor Gerhard Schrader an unusual early election. He declared that Germany faced “giant challenges” and that “our future and the future of our children is at stake.”

Merkel won power, but nearly blew a huge poll lead after her talk of deeper reform turned off voters. Kohler also talked less of economic change in later years and was strongly critical of financial markets during the banking and economic crisis — describing them as a “monster” that hadn’t yet been tamed.

Amid criticism that he appeared to have little to say after winning a second term, Kohler resigned in dramatically abrupt fashion on May 31, 2010. He cited criticism over a radio interview he gave following a visit to German troops in Afghanistan.

In that broadcast, he said that for a country with Germany’s dependency on exports, military deployments could be “necessary … in order to defend our interests, for example free trade routes.”

That was taken by many as relating to Germany’s unpopular mission in Afghanistan, although his office later said he was referring to anti-piracy patrols off the coast of Somalia.

Many wondered whether that was the real reason for the sometimes thin-skinned Kohler’s resignation, with critics speculating that he had simply become fed up with a lack of backing from Merkel — for whom his resignation was an embarrassment.