Ahead of his upcoming visit to Australia to headline the Supanova Gold Coast Pop Culture Expo on April 17-19, the 79-year-old reflected on the time Nimoy went in to bat for him.

In 1973, the classic show was being turned into an animated series, but Takei (Mr Sulu) and co-star Nichelle Norris (Uhura) were not cast as voice actors.

"When Leonard discovered that, he said 'diversity is what Star Trek is all about, and the two people that represent diversity the most are Nichelle and George, and if they're not going to be with the project, then this project isn't for me'," Takei said.

"Of course, Leonard was absolutely essential for the animated project, so they very interestingly found the money for Nichelle and me."

Takei said it showed the human side to the man famous for embodying the Vulcan Spock.

He said the outpouring of love for Nimoy following his death aged 83 on February 27 was entirely justified.

"The word extraordinary is often overused, but that really is appropriate for Leonard," he said.

"So much of what Spock is – the Vulcan greeting, for example, or the Spock pinch – was created by Leonard on the set."

Takei's own portrayal of USS Enterprise helmsman Mr Sulu earned him the unconditional love of Star Trek fans, but his popularity has soared over the past decade, during which time he came out as a gay man, married his longtime partner Brad Altman, became a vociferous supporter of LGBT rights and started a humourous Facebook page that now has more than 8 million followers.

Takei said he'd kept his sexuality secret for so long because he feared losing his acting career.

"The studio would have screenings with the press there, and I would take a female friend. After I took her home, I may have been at a gay bar later after that," he said.

"I was living a double life, I had my guard up all the time. It's a very exhausting, intense, torturous existence – and I did it until 2005."

Takei is now in as much demand off-screen as an activist for marriage equality.

He compares the fight for fairness for the queer community to one of his earliest experiences – being interned during World War Two simply because his grandparents had been Japanese.

"We had nothing to do with Pearl Harbour, we were Americans, and yet because we happened to look like them, we were imprisoned," he said.

"It was a combination of war hysteria and racism."

In 1988, then-president Ronald Reagan made a formal apology to the more than 100,000 Japanese-Americans who suffered in bitterly cold rural camps, or in Takei's case, swelteringly hot ones.

"There was a poignancy about that apology, because it was my father who felt the pain, anguish, humiliation and degradation of the internment the most," he said.

"He passed in 1979, so he never lived long enough to know that the government apologised for that horrible act."

Takei's Star Trek legacy combined with his role as an elder statesman of the internet mean he will no doubt be bombarded with fans when he appears at Supanova.

But on the eve of Star Trek's 50^th anniversary, he remains delighted by his role in it.

"This incredible longevity, this phenomenon, was created by the fans' devotion. It was not created by Gene Roddenberry or anybody, it was the fans," he said.

"So I see these conventions as a way to say thank you to the fans for their undying support in person. Like politicians we get to press the flesh."