Actor Haruo Nakajima speaks during an interview at his home in Sagamihara, near Tokyo, in 2014. (Junji Kurokawa/AP)

Haruo Nakajima, the Japanese actor who first portrayed Godzilla, the roaring, fire-spraying, Tokyo-demolishing, irradiated sea monster that launched a global franchise, died Aug. 7. He was 88.

The cause was pneumonia, his daughter Sonoe Nakajima told the Associated Press. No other details were immediately available.

Mr. Nakajima began his acting career after World War II as a stuntman in samurai movies, winning a small role as a bandit in director Akira Kurosawa’s 1954 drama “Seven Samurai.” But he would forever be associated with “Godzilla,” made that same year, in which a menacing, dinosaurlike creature lumbers through the Japanese capital, razing infrastructure and terrorizing the population.

He reprised the role in a dozen sequels as Godzilla went on to battle giant moths, armadillos and other foes, epitomizing campy filmmaking at its best — or worst. But the core of the original film was somber, an expression of the fears of a population that had endured the atomic bombings of Hiroshima and Nagasaki in 1945 and was alarmed by reports of radiation poisoning among fishermen exposed to hydrogen-bomb testing at sites off the Marshall Islands in the Pacific.

“Godzilla” was the brainchild of producer Tomoyuki Tanaka, who dreamed up a plot involving a sea creature resurrected from a deep sleep by the bomb testing. The film borrowed heavily from a recent American picture, “The Beast From 20,000 Fathoms,” but put a distinctly Japanese spin on the allegory.

Mr. Nakajima, who dressed in a rubber suit to play the original Godzilla, in 1966. (Kyodo/Reuters)

Mr. Nakajima recalled gleaning little sense of his “character” from the script.

“I had no idea what the role was or how the monster would move,” he told the Los Angeles Times 50 years later. “Even from the script, you couldn’t imagine the shape of the monster. I was thinking I’d be playing something like a huge frog, which is a popular type of character in Japanese ninja movies. I also thought it might be like a stage play where the actor is inside an animal costume, like two guys playing a horse.”

He went to a Tokyo zoo and studied the behaviors and motion of elephants and gorillas to imagine how Godzilla might have moved.

“There are not a lot of actors that you can compare him to,” said Akira Mizuta Lippit, a cinematic-arts professor at the University of Southern California. “He, in fact, invented the kind of acting that he then performed. In that sense, he’s absolutely unique. And he’s unique in ways that are important to understanding Japanese culture.”

Gojira, as the monster was called in Japan, derived its name from the word gorilla and kujira, a Japanese word for whale.

Scarcity of resources in postwar Japan made rubber and other malleable costume materials hard to come by. Tanaka’s Toho Studios created a colossal costume out of what Mr. Nakajima described as ready-mixed concrete, weighing more than 200 pounds.

“It was so heavy and hot, and with the lighting it was even hot just to touch it,” Mr. Nakajima said in a video interview earlier this year with the video network Great Big Story. “I was sweating all over my face, but I did the best I could.”

Japanese actor Haruo Nakajima speaks behind a gold statue of Godzilla in 2014. (AFP/Getty Images)

Allied occupying forces encouraged the rebooting of the Japanese film industry, but with caveats. The Japanese were not to produce movies about war or feudal Japan, nor were films to be critical of the United States.

“Godzilla” was a legacy of that policy. The monster became an unlikely scaly ambassador to Western audiences. Citizens of Tokyo were portrayed as pacifist victims, fearful of the monster that nuclear testing had brought to their neighborhoods.

Mr. Nakajima’s portrayal of Godzilla, with his claw-flailing stampedes, gave Japan one of the first icons of its economic reemergence, spawning a mini-industry of dolls, games and other toys. Besides its sequels, “Godzilla” inspired megafauna monster movies including “Pacific Rim” (2013).

Haruo Nakajima was born in Yamagata, Japan, on Jan. 1, 1929. Complete information on survivors was not immediately available.

Godzilla was not Mr. Nakajima’s only costumed character; he also played a pterodactyl-like animal in the 1956 film “Rodan” and the title gorilla in the 1967 film “King Kong Escapes.” But Godzilla, which he last portrayed in the 1972 iteration “Godzilla vs. Gigan,” was his piece de resistance.

“He was the Mona Lisa of monsters,” Mizuta Lippit said. “You never really knew if he’s good, or bad, or how good or how kind he is. At moments, he’s all of those things.”