According to the actor's wife, Susan Bay Nimoy, who confirmed his death, her husband's passing was due to the end stages of chronic obstructive pulmonary disease (CPOD). He was hospitalized earlier this week.
"I loved him like a brother," William Shatner, who played Captain Kirk alongside Nimoy in the Star Trek series, told ET in a statement. "We will all miss his humor, his talent, and his capacity to love."
This past year, Nimoy revealed that he was diagnosed with the lung disease that he said was the from years of smoking, though he had given up the habit decades earlier. In a series of tweets shared in January 2014, the Star Trek star encouraged every smoker to kick their cigarette habit, and even incorporated Spock's iconic "Live long and prosper" (LLAP) tagline into the message.
"I quit smoking 30 yrs ago. Not soon enough. I have COPD. Grandpa says, quit now!! LLAP," he wrote. "Smokers, please understand. If you quit after you're diagnosed with lung damage it's too late. Grandpa says learn my lesson. Quit now. LLAP."
Nimoy sent out his final tweet to his 1.1 million followers on Feb. 23, reading: "A life is like a garden. Perfect moments can be had, but not preserved, except in memory. LLAP."
A life is like a garden. Perfect moments can be had, but not preserved, except in memory. LLAP— Leonard Nimoy (@TheRealNimoy) February 23, 2015
Nimoy's co-stars, peers and fans are already paying their respects to the star via social media.