Masao Yoshida, the plant manager who led the fight to bring Japan’s Fukushima atomic station under control during the 2011 nuclear disaster, died July 9 at a hospital in Tokyo. He was 58.

The cause was esophageal cancer, according to a statement from Tokyo Electric Power Co., the operator of the Fukushima Daiichi nuclear plant. The illness was unrelated to the radiation exposure after the nuclear accident, according to Tepco, as Tokyo Electric is known.

Mr. Yoshida, an engineer by training, directed workers to stop the reactors from overheating after Japan’s strongest earthquake on record and an ensuing tsunami hit the plant on March 11, 2011, causing the worst nuclear disaster since Chernobyl in 1986. He stayed at the plant, helming the disaster response for almost nine months.

“I cannot imagine how hard it was for him,” Tatsujiro Suzuki, vice chairman of the Japan Atomic Energy Commission, said in an interview Tuesday. “He had to make a decision that most of the on-site workers should leave because the situation was getting worse and he also had to have some of his staff remain to work with him. That was probably the hardest decision he ever had to make.”

Mr. Yoshida stepped down Dec. 1, 2011, after having been hospitalized a few days earlier for an unspecified illness. Officials from Tepco disclosed Mr. Yoshida’s cancer eight days later.

Masao Yoshida, the manager of the Fukushima atomic plant, who stayed at his post to try to tame runaway reactors after the 2011 tsunami, died of cancer on July 9. (Japan pool/AFP/Getty Images)

After studying nuclear engineering at the Tokyo Institute of Technology, Mr. Yoshida joined Tepco in 1979, according to the utility. He was appointed head of the Fukushima Daiichi plant in June 2010.

As radiation levels spiked in the early days of the crisis, workers were pulled out of the plant, leaving behind what became known as the Fukushima 50, who risked their lives to bring the reactors under control.

On March 12, a day after the tsunami, Mr. Yoshida ignored an order from Tepco headquarters to stop pumping seawater into a reactor to try and cool it because of concerns that ocean water would corrode the equipment.

Tepco initially said it would penalize Mr. Yoshida even though Sakae Muto, then a vice president at the utility, said it was a technically appropriate decision. Mr. Yoshida received no more than a verbal reprimand after then-Prime Minister Naoto Kan defended the plant chief, the Yomiuri newspaper reported.

“I bow in respect for his leadership and decision-making,” Kan said Tuesday in a message posted on his Twitter account.

Mr. Yoshida thought several times that workers at the plant were going to perish, he told reporters who visited the Fukushima station on Nov. 12, 2011, the Mainichi newspaper reported. Mr. Yoshida had thought that plant operators might completely lose control as the meltdowns accelerated, he told reporters.

“If Yoshida wasn’t there, the disaster could have been much worse,” said Reiko Hachisuka, the head of a business group in Okuma town, home to the Fukushima Daiichi plant, and one of the Diet panel members who investigated the accident. His charisma made “workers at the Fukushima plant believe they could die for Yoshida,” she said.

The 2011 earthquake and tsunami left more than 18,000 people dead or missing and forced the evacuation of 160,000, eventually prompting the idling of all but two of Japan’s 50 functioning reactors for safety checks.

— Bloomberg News