Walter Koenig, best known for portraying Pavel Chekov in the Star Trek franchise, died from cardiopulmonary arrest, according to his death certificate.The document, obtained by People magazine on Tuesday, Nov. 3, lists chronic diastolic congestive heart failure as an underlying cause. Acute renal failure was also identified as a significant contributing condition.Walter Koenig died at 90 on Oct. 25. He was cremated five days later, on Oct. 30. His representative announced his passing on Oct. 26, saying the actor died at home in North Hollywood the previous night, surrounded by his daughter and niece.The 2019 Official Star Trek Convention Las Vegas - Source: GettyThe initial statement, issued by his representative, described his death as being “of old age.”“...Walter helped inspire audiences with his optimism, humor, and adventurous spirit. Beyond Star Trek, his long and distinguished career showcased his versatility as an actor and his genuine love for his craft.”The rep continued:“His remarkable talent continued to shine in his later years, most recently with his performance in the short film Mr. Fleischmann, for which he received the Platinum Award for Best Actor at the 2026 Independent Shorts Awards — a fitting recognition of a lifetime devoted to his craft.”Walter Koenig became a familiar face to generations of science fiction fans through his portrayal of Ensign Pavel Chekov on Star Trek: The Original Series, appearing from 1967 to 1969.His representative also highlighted his work beyond the franchise, including his performance in the short film Mr. Fleischmann. The role earned him the Platinum Award for Best Actor at the 2026 Independent Shorts Awards.2018 Star Trek Convention Las Vegas - Source: GettyThe statement also remembered Walter Koenig for his connection with fans, particularly through convention appearances and personal interactions over the years.“Walter’s legacy extends far beyond the screen. Through countless convention appearances and interactions with fans, he shared his kindness, wit, and appreciation with everyone fortunate enough to meet him. He understood what Star Trek meant to people and embraced the community that grew around it.”The rep went on:“On behalf of all of us, we extend our deepest condolences to Walter’s family, friends, colleagues, and the millions of fans whose lives he touched over the decades. Thank you, Walter, for the memories, the inspiration, and for boldly going where few have gone before. Rest in peace.”Tributes pour in for Walter Koenig after his death at 90Walter Koenig’s Star Trek co-star, William Shatner, took to his Instagram to pay tribute to the late icon. He described feeling “deeply saddened” by the late icon’s passing.“What I observed, and what so many fans have expressed over the years, was a man who genuinely loved the Star Trek community. At conventions, Walter was rarely content to remain behind a signing table. He preferred to be among the people who had kept Star Trek alive for so many decades. That kind of genuine connection is rare, and it will be remembered by everyone who came into contact with him.” View this post on Instagram Instagram PostAnother co-star, George Takei, also honored Walter Koenig in a heartwarming message. He narrated how he and Koenig became friends.“Walter and I met on the bridge of the Enterprise in the 1960s, and we stayed friends for nearly six decades.”He continued:“Walter was more than Chekov. He was a writer, a teacher, a thoughtful man, and a loyal friend.”Meanwhile, Adam Nimoy remembered Koenig as a "nice guy" and a pleasure to hang out with on the convention circuit, highlighting Koenig's role in the Original Series episode The Apple.Marina Sirtis described Koenig as a wonderful, kind, quiet, unassuming gentleman and shared memories from working with him on the film Inalienable.Creation Entertainment honored the late actor as the first Star Trek convention guest to grace their stages in 1979, citing his:"boundless energy, your scathing wit, your academic insight and your warm personality."