US actor George Takei has remembered his Star Trek co-star Walter Koenig as “a thoughtful man and a loyal friend” after his death aged 90.

Koenig was best known for starring in the original 1960s sci-fi series as Russian crewman Ensign Pavel Chekov, and for portraying Alfred Bester in space opera Babylon 5.

His death was announced in a Facebook post by talent agency Galactic Productions, which said he “passed of old age at home in North Hollywood last night surrounded by his daughter and niece”.

The message described Koenig’s legacy as an actor and praised his “talent, warmth, and unforgettable performances” which have “left a lasting mark on generations of fans around the world”.

Takei, 89, who played USS Enterprise helmsman Hikaru Sulu, said his “heart is heavy” as he paid tribute to his “dear friend” Koenig on Instagram alongside a picture of them.

“Walter and I met on the bridge of the Enterprise in the 1960s, and we stayed friends for nearly six decades,” he wrote.

“When Brad and I married in 2008, Walter stood beside us as our best man.

“Just last month, on Sept. 14, he turned 90, on the same day Brad and I celebrated our 18th wedding anniversary.

“I will always treasure that he and I shared that date.”

Takei continued: “Walter was more than Chekov.

“To the fans who loved him for so many years, thank you. He loved you too.

“Rest well, my dear friend. Keep navigating a steady course.”

Also among those paying tribute was TV director Adam Nimoy, the son of the late Leonard Nimoy – who played the half-alien science officer Mr Spock in Star Trek.

Nimoy posted a snap of Koenig from one of his “favourite” episodes of the sci-fi series and wrote: “So sad to hear about the loss of Walter Koenig.

“Such a nice guy and when we were on the convention circuit together a pleasure to hang out with.

“Here he is with Celeste Yarnall in ‘The Apple’, one of my favourites of the oddball episodes. Farewell.”

Koenig joined Star Trek for its second series in 1967, starring alongside Takei, Nimoy and William Shatner.

He reprised his role as the young Russian navigator in seven Star Trek films and wrote a book about the series titled Chekov’s Enterprise, which was published in 1980.

He also continued to appear on sci-fi fans’ screens in the 1990s, starring as villainous psychic Alfred Bester in hit series Babylon 5.

He continued to honour his Star Trek legacy with regular appearances at fan conventions and also voiced the son of his original character in the final season of Star Trek: Picard in 2023.

Koenig was married to actress Judy Levitt, who died in 2022.

Their son Andrew died in 2010, and he is survived by their daughter Danielle.