He’s the ex-cleaner who ended up playing a pirate in Game of Thrones. Now Lucian Msamati faces his biggest challenge yet – as the RSC’s first black Iago. He talks to Ryan Gilbey

Lucian Msamati cuts a swaggering figure in Game of Thrones as the pirate Salladhor Saan. Debonair with a whiff of debauchery, all jerkins and billowing shirts, he prowls the screen issuing frightful declarations like: “The one true God is what’s between a woman’s legs!”

Today, the 38-year-old, born in London but raised in Tanzania and Zimbabwe, has crossed over to the other side: directing. He sits behind a desk in a bright rehearsal room, watching intently as two women, scripts open in their laps, discuss a jazz trumpeter with whom they have both enjoyed a dalliance. Msamati rises sharply from his seat and leans across the table, torso straining against his checked shirt – at 5ft 5in, he is a small man but solid. “Pause,” he tells them calmly but insistently. “Remember, this isn’t Sunday teatime chit-chat. This is the elephant in the room.” The actors, Lynette Clarke and Angela Wynter, nod and have another crack at the scene in Boi Boi Is Dead, the first full-length play by the Zimbabwean-born poet and playwright Zodwa Nyoni.

As the play’s title suggests, the object of the women’s affections is otherwise detained. “It’s about grief,” Msamati tells me during lunchbreak. “This is a dysfunctional family coming to terms with death, but lacking the infrastructure to deal with it. Boi Boi was a proper superstar. But that has long since passed, and he hasn’t left much behind. We realise that he was actually quite selfish.” He grins. “He was a bit of a dick.”

Facebook Twitter Pinterest As Salladhor Saan in Game of Thrones Photograph: PR

Msamati has had a few surprises thrown at him by his cast. “You can do all the preparation in the world,” he says, “but on the first day, you can guarantee an actor will come up with something unforeseen.” He mentions cast member Andrew French’s approach to a moment of violence. “We were plotting our way and Andrew said, ‘I feel like when I’ve got the envelope in my hand, I just want to stuff it in her face!’” Msamati’s mouth falls open, startled. “I told him, ‘That’s it! Do that.’”

Soon it will be time for Msamati to concentrate on what will be his most taxing acting role yet: when he takes to the stage this summer in Othello, he will be the first black performer in the history of the RSC to play Iago. It’s a casting choice that adds a dangerous frisson to the character’s racist jibes about Barbary horses and black rams. Msamati has always maintained that he wants to be thought of as an actor, rather than a black actor, but he concedes that race will complicate this part.

“We were kicking ideas around in the workshop and something changed with me as Iago. Everyone said, ‘That works.’ The idea was to play with the discomfort of that. It is partly about race, but also about how people behave in the grip of jealousy. I’ve seen it happen in my own life. Certain words come out, even from friends’ mouths.You think, ‘Oh, so is that what I am? Where did that come from? I know that’s not you. But it must come from somewhere.’” Is he talking about racism? “Racism, yes. Or anything bubbling just below the surface.” He lifts his hand to his mouth and mimes the zipping and padlocking of his lips. “The important thing is we’re discovering new things. We’re going to get in a room and see what happens.”

Msamati spent four years as artistic director of Tiata Fahodzi, the British-African company (the name means Theatre of the Emancipated) that is co-producing Boi Boi Is Dead. Before that, he was with Over the Edge, the troupe he co-founded in Harare in the mid-90s, leading them around the world in productions he now characterises as “wild and passionate and full of mistakes – we did everything the hard way”. It was after the group’s 2001 Edinburgh fringe run that he stayed on in Britain, working as a cleaner while trying to forge an acting career.

Facebook Twitter Pinterest On right, in Clybourne Park. Photograph: Tristram Kenton

While his stage work includes Clybourne Park and the London riots play Little Revolution, and his TV credits include The No 1 Ladies’ Detective Agency and Doctor Who, the phenomenon that is Game of Thrones tends to eclipse everything else. He is well aware of the ardour of fans. “But it’s the work that’s fun. The freedom we are given to go for it, to dare. That’s the stuff that’s exciting. Not ‘Where’s my cappuccino?’ or ‘Why haven’t I got a bigger trailer?’” He releases a throaty chuckle. “The stories I could tell!”

• Boi Boi Is Dead is at West Yorkshire Playhouse, Leeds, 14 February-7 March, then Watford Palace theatre, 18-28 March