TOKYO (AP) -- Masao Yoshida, the man who led the life-risking battle at Japan's crippled nuclear power plant when it was spiraling into meltdowns, died Tuesday of cancer of the esophagus. He was 58.

Tokyo Electric Power Co. spokesman Yoshimi Hitosugi said Yoshida died at a Tokyo hospital. TEPCO officials said his illness was not related to radiation exposure.

Yoshida led efforts to stabilize the Fukushima Dai-ichi nuclear power plant after the March 11, 2011, earthquake and tsunami knocked out its power and cooling systems, causing triple meltdowns and massive radiation leaks.

Recalling the first few days when the three reactors suffered meltdowns in succession, Yoshida later said: "There were several instances when I thought we were all going to die here. I feared the plant was getting out of control and we would be finished."

Yoshida was an outspoken, tall man with a loud voice who wasn't afraid of talking back to higher-ups and was known to his workers as a caring figure. Even then-Prime Minister Naoto Kan, who was extremely frustrated by TEPCO's initial lack of information and slow handling, said after meeting him that Yoshida could be trusted.

On March 12, after Unit 1 reactor building exploded following a meltdown, Yoshida kept pumping in sea water into the reactor to cool it, ignoring an order from the TEPCO headquarters to stop doing so as Kan feared a possibility of sea water triggering a fission chain reaction. Yoshida was initially reprimanded for disobeying the order from above, but later praised for his judgment that eventually helped keep the reactor from turning worse.

"I bow deeply in respect to his leadership and decisiveness," Kan said in his Twitter entry Tuesday.

Kunio Yanagida, former member of a government-commissioned accident probe panel who interviewed Yoshida for 10 hours, said his death is a major loss for future investigations into the disaster at the plant, which hasn't been fully examined due to high levels of radiation.

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Yoshida studied nuclear engineering at the Tokyo Institute of Technology and joined TEPCO in 1979. He worked in the company's nuclear department before landing a top job at the Fukushima Dai-ichi a year before the crisis.

Yoshida stepped down as plant chief in December 2011, citing the cancer, after workers had begun to bring the plant under control.

Yoshida had brought workers together and kept their spirits up to survive the crisis, and had expressed hopes of returning to work for Fukushima's recovery even after falling ill, TEPCO President Naomi Hirose said.

"He literally put his life at risk in dealing with the accident," Hirose said in a statement. "We keep his wishes to our heart and do utmost for the reconstruction of Fukushima, which he tried to save at all cost."