Days after a torrential downpour collapsed two aging dams and unleashed a rushing wall of water that swept parts of the Libyan city of Derna and thousands of its people into the sea, the military strongman who rules the area came for a quick visit.

Khalifa Hifter, the 79-year-old renegade commander and longtime C.I.A. asset shook hands with soldiers, took a brief drive through Derna’s muddy streets and flew off in a helicopter.

The disaster that struck Derna on Sept. 11 has drawn renewed international attention to Mr. Hifter and his so-called Libyan National Army, a military coalition that controls the eastern half of the divided North African nation with an iron fist.

More than a week after the disaster, as rescue efforts shift to the long and costly work of caring for the displaced and helping the city recover, Mr. Hifter’s tight hold over eastern Libya has made it clear that he will be the overall arbiter of the aid operation in the oil-rich country.

That makes many longtime Libya watchers, including some who have spent time with Mr. Hifter, nervous.

He oversees what is effectively a military dictatorship that competes for power with an internationally recognized government in the western half of Libya that is based in Tripoli, the capital. He has enriched and empowered himself and his sons while failing to provide basic services or maintain critical infrastructure, like the dams that burst last week, analysts and diplomats say. Human rights groups have accused his forces of grave abuses and potential war crimes.

His overarching goal appears to be to rule all of Libya, so much so that as United Nations-sponsored peace talks were set to begin in 2019, he launched a military assault on Tripoli with backing from Russia’s Wagner mercenary group. The attack ultimately failed.

Since last week’s disaster, Mr. Hifter has tried to cast himself in a more benevolent light.

“He’s the savior. He is not to blame for what happened,” said Tarek Megerisi, a Libyan analyst at the European Council on Foreign Relations, summarizing Mr. Hifter’s messaging. “He has dominated the response, so there is military deployed everywhere around Derna so he can look like he’s securing the city.”

Mr. Hifter has given his sons prominent roles in his power structure. One of them, Al-Siddiq, has modeled himself as a politician. Another, Saddam, leads a powerful branch of Mr. Hifter’s forces and is overseeing the aid operation for Derna.

In recent days, those forces have refused to let foreign journalists enter eastern Libya to report on the crisis and restricted the movements of those already there. Checkpoints have been set up at entrances to the city. On Tuesday, a United Nations spokeswoman said that a U.N. team had not been allowed to travel to Derna, although other teams continued to work there.

Further complicating the aid effort is a history of bad blood between Mr. Hifter and Derna.

After local Islamist fighters defeated a franchise of the Islamic State terrorist group in Derna in 2015, they resisted an effort by Mr. Hifter’s forces aimed at taking over control of the city. After long battles, the Libyan National Army seized it in 2018.

Mr. Hifter has done little to help the city fix the damage left by the battles and blocked its local elections, appointing as mayor a nephew of Aguila Saleh, a political ally of Mr. Hifter’s and the speaker of Libya’s Parliament, which is part of the eastern Libya administration.

On Tuesday, hundreds of Derna residents protested in the destroyed city, calling for the ouster of Mr. Saleh for his role in an administration they said has failed to keep them safe. They did not chant against Mr. Hifter, and it remains to be seen whether the disaster in Derna will shake his rule.

A former Western diplomat who worked in Libya said Mr. Hifter is well-placed to benefit from the crisis because he oversaw the only structure that could do a vast aid operation. That could strengthen his ties with international aid organizations, further entrenching his control, the former diplomat said, speaking on condition of anonymity.

Mr. Hifter has long been a deft survivor of Libya’s brutal politics. He was a young army officer in 1969 when he participated in a coup by Col. Muammar el-Qaddafi that toppled the monarchy and paved the way for Colonel el-Qaddafi to become Libya’s supreme ruler for four decades.

The two men fell out after the coup and Mr. Hifter fled to the United States, where he lived in Virginia for two decades as a C.I.A. asset and fruitlessly explored ways to oust his former comrade.

He returned to Libya in 2011, when the Arab Spring protests erupted across the country and became a leader in the rebel movement that, alongside a NATO military intervention, toppled and killed Mr. el-Qaddafi.

In the years since, Mr. Hifter has enhanced his power. A new civil war that began in 2014 eventually put him and the Libyan National Army, or L.N.A., in charge of eastern and southern Libya, where he has set up a shadow administration in opposition to the government in Tripoli.

Egypt, Jordan, Russia and the United Arab Emirates have backed his rise to varying extents, mainly because they view him as the best candidate to stabilize the country by cracking down on extremist groups and political Islamists.

But his efforts to expand his control have often been brutal, and rights groups have accused his forces of torturing and summarily executing captured foes and brutalizing civilians suspected of disloyalty.

His administration is widely regarded as more interested in reaping profits for Mr. Hifter and his cronies than in improving the lot of Libyans.

“It is an administration that focuses first and foremost on territorial control and repression,” said Wolfram Lacher, a Libya researcher at the German Institute for International and Security Affairs. “It is also an administration that tries to extract as many resources as it can from these areas.”

In addition to the income earned from controlling most of Libya’s oil production, Mr. Hifter’s forces have made money from drug smuggling, trafficking migrants and disassembling eastern Libya’s infrastructure to sell for scrap, Mr. Lacher said.

Since the Derna disaster, analysts have mentioned Mr. Hifter’s focus on power accumulation over governance as part of why nothing was done to shore up the aging dams that experts knew posed a threat and had warned about in advance.

“The reason we got here is because, effectively, Libya has not had a functioning government for a long time. So the money that could have been spent on governance has been spent on the L.N.A.,” said Tim Eaton, a researcher at Chatham House, a research group.

Mr. Hifter’s strongman status has not made him an international pariah. He has received military support from the United Arab Emirates, Egypt and Russia and met with high-level Western officials, angering Libyans who say that such meetings bolster the standing of corrupt, unelected politicians.

President Emmanuel Macron of France welcomed Mr. Hifter in Paris in 2020 to discuss a possible Libyan cease-fire, and William J. Burns, the head of the C.I.A., met with him and the head of the Tripoli-based government during a visit to Libya in January.

Analysts said that Western officials had no illusions about Mr. Hifter’s aims, but considered him a necessary interlocutor in a messy country about issues including counterterrorism, oil exports and efforts to stem migration to Europe.

“They are not convinced that the alternative will be better, and what he does is provide a known quantity in his consolidation over elements in eastern Libya,” said Mr. Lacher, the researcher. “He has become a fact on the ground that you’ll have to deal with until he dies.”

Mr. Hifter has leveraged issues the West cares about to solidify his power.

Recently, the number of migrants departing for Europe from eastern Libya surged, a phenomenon analysts said could not have happened without the involvement of his forces.

In May, Mr. Hifter traveled to Rome for discussions with Prime Minister Giorgia Meloni and other senior officials.

The top item on the agenda: Restricting migration from Libya to Europe.

Vivian Nereim contributed reporting from Riyadh, Saudi Arabia.