It’s a genre dominated by white, straight males, so American actress Nafessa Williams admits she was moved to tears when she pulled on her costume for the first time to play a black, lesbian superhero. “It was a moment,” she says. “I mean, I’m representing a whole group of people who need to see themselves on TV.”

Williams plays Thunder in the hit television series Black Lightning – and is in London this week to promote its second series and hopefully convert more Britons to what she admits is “not your typical superhero show”.

“Yes, we’re wearing costumes but we’re not fighting aliens or creatures in an alternative universe,” she says. “We’re fighting real-life issues that are happening within our country, in our inner cities. Police brutality, gang crime, drug crime, social injustice – and we’re shedding light on it.”

Set in the fictional city of Freeland, the show, says Williams, is first and foremost about a family trying to save its community. A community overrun by the “100 Gang” – notorious for drug and sex trafficking. “It’s not until you see us in costumes that you realise, oh, this is a superhero show as well,” she says.

Williams plays Anissa Pierce, a medical student and black-rights activist who learnt of her superhuman powers in the first series. She is one of three lead characters in the same family. Jefferson Pierce (played by Cress Williams) is her father and, secretly, Black Lightning, the eponymous superhero of the comic strip first published in 1979 by DC Comics – the birthplace of Superman, Batman and Wonder Woman.

In this TV adaptation Pierce is trying to give up his electrically charged powers and change society through peaceful means, as a high-school principal. But his eldest daughter Anissa vows to fight. “I’m sick and tired of being sick and tired,” she says, echoing the words of civil rights hero Fannie Lou Hamer. “Anissa is so bold, and so unapologetic. I’ve found myself being an activist through my character. She’s inspiring the hell out of me,” says Williams.

Like all superheroes, Anissa (aka Thunder) has a love interest, but hers is no dweeby college boy. This superwoman is a lesbian with a girlfriend named Grace Choi, a half-Amazonian Asian-American played by Canadian actress Chantal Thuy. It is a throwback, perhaps, to Wonder Woman, who many believe was drawn originally as a gay hero but who has morphed back to heterosexuality over time. In the 2017 film, for example, Wonder Woman’s love interest is an American serviceman.

Not Thunder though. Her emotional battle is coming out as a superhero, not as a lesbian. As a gay woman, she is open, happy and comfortable – with supportive parents. A big part of season two, though, will explore her love life further. “I like the idea of continuing that relationship [with Grace], seeing where it goes,” Williams says. “I think it’s very real. and people want to relate to issues that they’re going through themselves.”

She tells how a teenager recently approached her and thanked her for playing a strong, black, gay woman. “She said that after seeing Anissa she now feels normal being a lesbian. It’s pretty cool because as a young black girl I didn’t have a superhero to look up to – there was no one who looked like me,” she says.

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Williams grew up in Philadelphia and briefly pursued a career in law, even working in a homicide department. She got fired though, after going without permission to an audition. Inspired in part, she says, by fellow Philadelphian Will Smith, Williams committed to carving a career in acting. She played Jade in last year’s Twin Peaks reboot, but Thunder has been her breakthrough role.

Now that the characters have been developed she hopes the show will “take it up a notch”. Her younger sister in the series, Jennifer (played by China Anne McClain) is the third key character and will have her own coming-of-age superhero story line in season two. “We can hit the streets together and fight crime, that will definitely be cool,” Williams says.

But taking on the bad guys is secondary, she believes, to the wider theme of communities struggling to find ways to cope. “I hope it will inspire other families to overcome their issues,” she says. “We all have that superhero inside us, but it’s about tapping into it and embracing it and owning it.”

Black Lightning is available on Netflix. Season 2 is expected to air next year