Nguyen Phu Trong, the hard-line general secretary of Vietnam’s Communist Party who presided over his country’s economic and geopolitical transformation, and reshaped its leadership with his “blazing furnace” anticorruption campaign, died on Friday at a hospital in Hanoi. He was 80.

His death was announced by the official Nhan Dan newspaper, which said that Mr. Trong had died of “old age” and an unspecified serious illness.

Speculation had swirled in January about Mr. Trong’s health after he skipped meetings with several foreign leaders. The seriousness of his illness became clear on Thursday, when the party announced that he would step back from his duties to focus on his health, and that President To Lam, a former security minister, would take over his responsibilities.

For 12 years, Mr. Trong sat at the apex of power in Vietnam’s Communist hierarchy. He served an unprecedented three terms as party chief and nearly three decades in the Politburo. He consolidated power in one of the world’s few remaining Communist dictatorships, significantly weakening the collective form of leadership that previously characterized the country’s Communist Party.

His death left no obvious successor.

“He was the most powerful leader in Vietnam after the Vietnam War,” said Nguyen Khac Giang, a visiting fellow at the ISEAS — Yusof Ishak Institute in Singapore. “I think anyone who will be chosen as the next leader of Vietnam will face an uphill battle in having the same kind of authority that Nguyen Phu Trong had.”

Mr. Trong represented a conservative Marxist-Leninist faction within the party, which includes another faction seen as more pragmatic and moderate. His death is likely to raise hopes in the West that a less doctrinaire leader could emerge. Mr. Trong, the only one in the 18-member Politburo who grew up during the Vietnam War, was a generation older than many of his peers.