Ebrahim Raisi, Iran’s president and a top contender to succeed the nation’s supreme leader, was killed on Sunday in a helicopter crash. He was 63.

A conservative Shiite Muslim cleric who had a hand in some of the most brutal crackdowns on opponents of the Islamic Republic, Mr. Raisi was a protégé of Iran’s supreme leader, Ayatollah Ali Khamenei, and a devoted upholder of religious rule in the country.

Mr. Raisi’s presidency was shaped by two major events: the 2022 nationwide uprising, led by women and girls, demanding the end to the Islamic Republic’s rule and the government’s brutal crushing of that movement; and the current Middle East war with Israel, with which it had a long history of clandestine attacks.

As the president under Iran’s political system, Mr. Raisi did not set the country’s nuclear or regional policy. But he inherited a government that was steadily expanding its regional influence through a network of proxy militia groups and a nuclear program that was rapidly advancing to weapons-grade uranium enrichment levels following the United States’ exit from a nuclear deal.

Mr. Raisi endorsed and supported both of these policies and viewed them as essential for Iran to maintain its influence in the region and to exercise leverage over the West.

His death came as a yearslong shadow war became one of direct confrontation in the wake of Israel’s military assault on Gaza in retaliation for the Oct. 7 Hamas attacks on Israel.