In 2015, with France and Italy pushing to ease the terms of austerity imposed on Greece, Mr. Schäuble circulated an alternative proposal: Greece could temporarily exit the eurozone. That prospect alarmed France, Italy and Greek’s left-wing government enough that they backed down.

He was unpopular elsewhere, too.

“Schäuble crystallized this growing gap between the so-called peripheral Europe and the core Europe,” said Constantin Gurdgiev, an adjunct finance professor at Trinity College Dublin. “As a result of this, he was loathed not just in Greece, and not just in Ireland, but in the likes of Italy, Spain, Portugal and Cyprus.”

Mr. Schäuble was often caricatured as an uncompromising disciplinarian, but he belonged to a generation that saw the European Union not just as an economic convenience but as a bulwark against the wars that devastated the Continent early in the 20th century. He regarded crises as a chance to push closer to something resembling a United States of Europe.

“We can only achieve a political union if we have a crisis,” Mr. Schäuble said in an interview in 2011.

At home, he has been a fixture in German politics for more than 40 years, dating to the period when Helmut Kohl was chancellor and Germany was still divided between East and West.

Mr. Schäuble has survived innumerable crises, including an attempt on his life in 1990 that left him in a wheelchair. In 2000, a campaign finance scandal forced him to step aside as chairman of the Christian Democrats, paving the way for Ms. Merkel’s ascent. She became chairwoman of the party at the time, and in 2005 rose to become chancellor.

Still, Mr. Schäuble often rated higher than Ms. Merkel in opinion polls. His insistence on balanced budgets, though criticized by economists, was extremely popular with debt-averse Germans. At conventions of the Christian Democrats he was greeted like a rock star, and his comments could move financial markets.