Thanks to “Star Trek,” George Takei is known to TV and film fans as Mr. Sulu of the U.S.S. Enterprise. Less known is his role in a shameful chapter in American history.

He can still remember vividly the day when, at age 5, his parents got him up early while they furiously packed suitcases. Out the front window, he saw two soldiers marching up the driveway, “with bayonets on their rifles,” he says. Takei and his family were among 120,000 Japanese Americans imprisoned in U.S. internment camps during World War II. They lost their homes and jobs for no other crime than being the wrong ethnicity. “There had been no reports of sabotage or spying by Japanese Americans,” but that just made authorities more suspicious, Takei says. “The absence of evidence was the evidence.”

Takei’s story inspired “Allegiance,” a new musical starring Takei (in his Broadway debut) and Tony Award winner Lea Salonga, with music and lyrics by Jay Kuo, and book by Kuo, Marc Acito and Lorenzo Thione. It opened at the Longacre Theatre in November.

Takei plays both a wise, gentle immigrant, and a bitter, grizzled World War II veteran. In real life, he also has multiple roles — as a civil and gay rights activist and social media megastar (with nearly 2 million Twitter followers). He and his husband live in Los Angeles.

How does it feel — your Broadway debut?

Well, I’m a theater actor from my teens. But Broadway — being on that big stage — is a major experience at age 78. But more important to me is the story. It’s my childhood. I was imprisoned by my own government, and that shaped who I am today.

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Why a musical? Did you consider telling this story as a play?

Yes. But one evening my husband, Brad, and I went to see “Forbidden Broadway,” the off-Broadway satire on musicals. Two people sat in front of us — and recognized my voice. It was this gifted composer and lyricist, Jay Kuo, and his friend Lorenzo Thione. We chit-chatted at intermission. The next night we went to see “In the Heights,” Lin-Manuel Miranda’s musical about the Puerto Rican community. As we sat down, we noticed two arms waving — Jay and Lorenzo. Brad whispered, “I think they’re stalking us.” (He chuckles.)

In the first act, a father has a song called “inútil” — useless — about how he wanted to help his daughter go to college but couldn’t afford it. That song was so moving, and reminded me of a conversation I’d had as a teenager with my own father. I’d been reading civics books and couldn’t find anything about our incarceration — this was back in the ’50s. It was after dinner — things became heated — and I said, “Daddy, you led us like sheep to the slaughter into the internment camp.” And suddenly the conversation stopped. My father was silent. I immediately sensed that I’d hit a nerve. After a long silence, he said, “Well, maybe you’re right.”

He went into the bedroom and closed the door. I felt awful. I’d hurt this man who’d lost everything in the middle of his life, and was struggling to make a life for his children. I wanted to apologize . . . but didn’t. That’s haunted me ever since. The song reminded me of that conversation. I was bawling.

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Understandable.

Yes. Also — I’m a weeper. (He chuckles.) After the show, we went out for drinks with Jay and Lorenzo and I talked about the internment. And Jay said it’s gotta be a musical. Music hits the heart so profoundly. And Japanese Americans tend to contain what they feel — the deep hurts. With a song, you can express that. Being a musical theater fan, I agreed. So it’s like it was preordained.

And how’d you and Brad meet?

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In the 1980s, at an L.A. running club. He’d run two marathons. I’d run none. So I asked him to train me, and during the course of training . . .

Were you really interested in marathons or did you have ulterior motives?

Ulterior motives. (He laughs.)

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Did you ever run a marathon?

I’ve run six.

So his training worked.

Yes. And I’ve been well-trained for 28 years.

You’re also a social media sensation. What’s your secret?

I have my sci-fi geeks and nerds as my core following. But when we started developing “Allegiance,” we realized that chapter of American history is little known. How to raise awareness? Well . . . social media is it. Through trial and error, I found what works. Humor — and being topical — gets the most “likes” and “shares.” Now it’s gotten so big, we’ve added interns to keep it all going. We call them Team Takei. And it keeps growing and growing.