A bit more than three years after Meir Dagan was forced to end his long tenure as director of Israel’s intelligence service, the Mossad, he showed up at a discussion of the Middle East filled with contempt for the Israeli prime minister, Benjamin Netanyahu, who he feared was on the cusp of bombing Iran’s nuclear facilities.

“There is no one to stop him anymore,” Mr. Dagan told me at Harvard University in spring 2014.

Mr. Dagan had long argued that by pushing him and other intelligence and military leaders out of office, Mr. Netanyahu was seeking to silence those who argued that there were better ways to deter Iran from getting the bomb than attacking the country’s facilities.

At best, Mr. Dagan said at Harvard, an Israeli bombing run would provide an illusory solution, temporarily flattening those facilities, only to have them return, this time deep underground. The result, the spymaster and former soldier argued, would be disastrous for the state of Israel.

Mr. Dagan, who died on Thursday after struggling for several years with a liver transplant that never quite succeeded, could hardly be accused of being soft on Israel’s enemies. He ranked among the most brutal warriors of the modern Middle East. He famously kept a photograph of his grandfather, kneeling on the ground before his Nazi captors moments before he was killed. Mr. Dagan would show it to visitors, a personal “never again” memento that seemed to explain the ease with which he organized the elimination of Israel’s enemies.