Walter Koenig, the actor best known for portraying Ensign Pavel Chekov on the original "Star Trek" television series, died Sunday at the age of 90.

Koenig's agent confirmed the news to ABC News, marking the end of a career that spanned decades and left a significant impact on "Star Trek" fandom. His passing was also shared by former co-star George Takei via an online post on Monday.

"Walter was more than Chekov. He was a writer, a teacher, a thoughtful man, and a loyal friend," Takei wrote, expressing his grief. Koenig's agent, Zachery McGinnis, stated that the actor "passed of old age at home in North Hollywood last night surrounded by his daughter and niece."

The actor's agent added that Koenig's "talent, warmth, and unforgettable performances left a lasting mark on generations of fans around the world."

Born on September 14, 1936, Koenig had a notable television career before joining the "Star Trek" universe. He appeared in shows such as "The Alfred Hitchcock Hour," "The Lieutenant," and "I Spy." His role as the young, Russian navigator Ensign Pavel Chekov was introduced in the second season of "Star Trek" in 1967, a character created to appeal to younger audiences.

Koenig himself noted in a 2013 interview that he had not seen "Star Trek" prior to auditioning for the role. He explained that the character was added after the show's debut, with producers seeking an actor who could connect with viewers aged 8 to 14, similar to the appeal of Davy Jones of The Monkees.

"Star Trek" proved to be a pivotal moment in Koenig's career. In a 1984 "Good Morning America" interview, he reflected on the show's profound effect, suggesting it was instrumental in his continued pursuit of an acting career and enabling him to explore other industry ventures like writing and directing.

Following his "Star Trek" tenure, Koenig continued to work in television, with appearances in series like "Columbo" and "The Starlost." He reprised his iconic role as Chekov in the 1979 film "Star Trek: The Motion Picture" and later in "Star Trek II: The Wrath of Khan" (1982), alongside other original cast members.