LOS ANGELES >> In 1975, Leonard Nimoy published an autobiography with the defiant title, “I Am Not Spock.” Two decades later, he bowed to fate with “I Am Spock,” a revisionist sequel.

But for Trekkies and even casual “Star Trek” viewers, Nimoy was always the coolly composed science officer with the pointed ears and an unwavering belief in logic.

He played a variety of other stage and screen roles, wrote poetry and pursued photography, but Nimoy’s portrayal of Mr. Spock remained indelible and inescapable.

It wasn’t just the trademark ears or the steeply arched eyebrows — which rose higher when Spock was confronted with disconcerting emotion — or the impressive divided-finger salute or the “Live long and prosper” catchphrase.

It was how Nimoy staunchly turned what could have been a caricature into a dignified, inspiringly intellectual and even touching figure, a half-human, half-Vulcan who was a multicultural and multiethnic touchstone, well before it was hip.

For Americans and others who witnessed 1969 U.S. moon landing, and for generations of geeks to come, Spock and “Star Trek” reinforced the power of science and space exploration.

Nimoy died Friday of end-stage chronic obstructive pulmonary disease at his Los Angeles home, with family at his side, said his son, Adam Nimoy. He was 83.

The reaction was swift, on Earth and in space.

“I loved him like a brother. We will all miss his humor, his talent, and his capacity to love,” said Shatner, whose often-emotional Captain Kirk was balanced by the composed Nimoy.

“Live Long and Prosper, Mr. #Spock!” tweeted Italian astronaut Samantha Cristoforetti, aboard the International Space Station.

George Takei, Mr. Sulu of “Star Trek,” called Nimoy a great man and friend.

“We return you now to the stars, Leonard. You taught us to ‘Live Long and Prosper,’ and you indeed did, friend,” Takei said.

In a 2009 interview with The Associated Press, Leonard Nimoy recalled how an early stage role left him “obsessed” with pursuing work that had a social impact.

“I’ve fulfilled that dream, including ‘Star Trek,’ for that matter,” he said. “If that’s part of the legacy, then I’m very pleased with that. I would hope the work I chose to do had some reason for being done other than just simply being a job.”

He said he hoped his work helped people understand their lives and the world.

After “Star Trek” ended, the actor immediately joined the hit adventure series “Mission Impossible” as Paris, the mission team’s master of disguises.

From 1976 to 1982, he hosted the syndicated TV series “In Search of … ,” which attempted to probe such mysteries as the legend of the Loch Ness Monster and the disappearance of aviator Amelia Earhart.

He played Israeli leader Golda Meir’s husband opposite Ingrid Bergman in the TV drama “A Woman Called Golda” and Vincent van Gogh in “Vincent,” a one-man stage show on the troubled painter’s life. He continued to work well into his 70s, playing gazillionaire genius William Bell in the Fox series “Fringe.”

He also directed several films, including the hit comedy “Three Men and a Baby” and appeared in such plays as “A Streetcar Named Desire,” ”Cat on a Hot Tin Roof,” ”Fiddler on the Roof,” ”The King and I,” ”My Fair Lady” and “Equus.” He also published books of poems, children’s stories and his own photographs.

But he could never really escape the role that took him overnight from bit-part actor to TV star. And in a 1995 interview, he sought to analyze the popularity of Spock, the green-blooded space traveler who aspired to live a life based on pure logic.

People identified with Spock because they “recognize in themselves this wish that they could be logical and avoid the pain of anger and confrontation,” Nimoy concluded.

“How many times have we come away from an argument wishing we had said and done something different?” he asked.

In the years immediately after “Star Trek” left television, Nimoy tried to shun the role. But he eventually came to embrace it, lampooning himself on such TV shows as “Futurama,” ”Duckman” and “The Simpsons,” and in commercials.

He became Spock after “Star Trek” creator Gene Roddenberry was impressed by his work in guest appearances on the TV shows “The Lieutenant” and “Dr. Kildare.”

The space adventure set in the 23rd century had an unimpressive debut on NBC on Sept. 8, 1966, and it struggled during its three seasons to find an audience other than teenage boys. It seemed headed for oblivion after it was canceled in 1969, but its dedicated legion of fans, who called themselves Trekkies, kept its memory alive with conventions and fan clubs and constant demands that the cast be reassembled for a movie or another TV show.

Trekkies were particularly fond of Spock, often greeting one another with the Vulcan salute and motto, “Live Long and Prosper,” both of which Nimoy was credited with bringing to the character. He pointed out, however, that the hand gesture was actually derived from one used by rabbis during Hebraic benedictions.

When the cast was reassembled for “Star Trek — The Motion Picture,” in 1979, the film was a huge hit, and five sequels followed. Nimoy appeared in all of them and directed two. He also guest-starred as an older version of himself in some episodes of the spinoff TV series, “Star Trek: The Next Generation.”

In 2009, he was back in a new big-screen version of “Star Trek,” this time playing an older Spock who meets his younger self, played by Zachary Quinto. Critic Roger Ebert called the older Spock “the most human character in the film.”

Among those seeing the film was President Barack Obama, whose even manner was often likened to Spock’s.

“Everybody was saying I was Spock, so I figured I should check it out,” Obama said at the time.

Upon the movie’s debut, Nimoy told the AP that in his late 70s he was probably closer than ever to being as comfortable with himself as the logical Spock.

“I know where I’m going, and I know where I’ve been,” he said. He reprised the role in the 2013 sequel “Star Trek Into Darkness.”

Born in Boston to Jewish immigrants from Russia, Nimoy was raised in an Italian section of the city where he said he felt the sting of anti-Semitism growing up.

At age 17, he was cast in a local production of Clifford Odets’ “Awake and Sing” as the son in a Jewish family.

“This role, the young man surrounded by a hostile and repressive environment, so touched a responsive chord that I decided to make a career of acting,” he said later.

He won a drama scholarship to Boston College but eventually dropped out, moved to California and took acting lessons at the Pasadena Playhouse.

Soon he lost his “Boston dead-end” accent, hired an agent and began getting small TV and film roles.

After service in the Army, Nimoy returned to Hollywood, working as taxi driver, vacuum cleaner salesman, movie theater usher and other jobs while looking for acting work.

In 1954, he married Sandra Zober, a fellow Pasadena Playhouse student, and they had two children, Julie and Adam. They divorced, and in 1988 he married Susan Bay, a film production executive.

Last year, Nimoy used Twitter to announce he had pulmonary disease. He linked it to smoking, a habit he said he quit 30 years before. In January, he tweeted: “Don’t smoke. I did. Wish I never had.”

Besides his wife, son and daughter, Nimoy is survived by his stepson, Aaron Bay Schuck. Services will be private, Adam Nimoy said.

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AP Television writer Frazier Moore in New York and AP Aerospace writer Marcia Dunn in Cape Canaveral, Florida, contributed to this report. This story contains biographical material compiled by late AP Entertainment Writer Bob Thomas.