George Takei is still best known for playing Mr Sulu, the self-possessed helmsman of the starship Enterprise. But Takei has always been more than a mere pilot (and astrophysicist, swordsman, botanist, etc). He has long been active in Asian-American advocacy and more recently has campaigned for marriage equality, too.

George Takei: 'I couldn't reconcile American ideals with what I knew'

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This fall, Takei is making his Broadway debut in Allegiance, a musical he helped to inspire. Takei plays both the kindly grandfather Ojii-chan and an older version of his grandson, Sam Kimura, the show's hero. (The younger Sam is played by Telly Leung.) Sam and his family are Japanese Americans and after the attacks on Pearl Harbor, they are sent to an internment camp, just as Takei's own family was. While reviews have been mixed, audience response has been tearful and enthusiastic.

On a recent weekday morning, Takei answered questions about the musical in his stately baritone. He was never less than gracious, even as he disagreed – forcefully and specifically – with the Guardian's review of the show. He discussed the life experiences that inspired the piece, his continuing advocacy and what it feels like to play to a house of Star Trek fans.

When did it occur to you that the internment of Japanese Americans might be material for a musical?

It's been my life mission to raise the awareness. We can't learn from history if we don't know our history and so many Americans don't know this chapter of American history. So from my early 20s on, I've been on speaking tours and founded a museum, the Japanese American National Museum.

But my personal passion is musical theater. To be able to merge my personal passion with my life's mission has been the most fulfilling thing in my life.