When you’re the youngest of 10 children, as the French actor Tahar Rahim is, you have to be quick to secure the best of your siblings’ hand-me-downs. One of Rahim’s best finds came as a 16-year-old, when he spotted a book on the night table of an older brother. It was Serpentine, Thomas Thompson’s 1979 true crime investigation of the life and crimes of Charles Sobhraj, a confidence man-turned-serial killer who brazenly left a string of bodies across Asia in the mid-1970s.

“I read it very quickly,” says Rahim, who more than two decades on can elicit the mix of fascination and fear that overcame him. “As I already wanted to be an actor, the fact that Sobhraj is changing identities all the time, plus was French, made me feel like he was an actor. I fantasised about playing him.”

The desire to play Sobhraj, whose public notoriety came to match his transgressions, never left the 39-year-old Rahim, who found fame in 2009 as the internationally acclaimed star of A Prophet, Jacques Audiard’s masterful French jailhouse crime film. When he opened an e-mail from his agent in 2019 and read an outline for a BBC/Netflix scripted co-production about a real life “murderer” and “manipulator” he was intrigued. Then Rahim scrolled down some more and saw that the character he’d been offered was Charles Sobhraj.

“Let’s call that fate,” says a laughing Rahim, sitting in a friend’s Parisian office on a chilly morning so as to both make use of the better internet access and keep the two young children he has with his wife and A Prophet co-star, Leila Bekhti, from crashing our video call.

When Rahim subsequently met the project’s principals, director Tom Shankland and screenwriter Richard Warlow, he enthused to the British duo about his connection to Sobhraj’s story. After he left, they later told Rahim, the two debated whether he was telling the truth or was spinning a tale to help secure the part. Eventually Shankland told Warlow, “You know, if this guy is lying to us he’s the right guy, because I totally believe him.”

Two years on and the resulting eight-part series, The Serpent, confirms that verdict. Rahim is both magnetic and malignant as Sobhraj, the son of a Vietnamese mother and an Indian father who was educated in France and graduated from thieving to drugging and murdering naïve young travellers on tourism’s “Hippie Trail” across Asia in the 1970s. Charming when he befriends those in need, callous when he kills them, Rahim’s mastermind is an instrument of inscrutable evil who draws victims in.

“I found it very hard to get connected to him. How could you? He’s a sociopath with no empathy,” Rahim says. “I need to find a connection with all of my characters. I tried so hard and I couldn’t, so what I did this time for the first time I tried to build my character from the outside: his look, the way he talks, the way he behaves with people.”

Set mainly in Bangkok, the series doesn’t settle for true crime recreations. While it can be grippingly tense, the narrative studies Sobhraj from multiple perspectives. There’s his girlfriend, Marie-Andree Leclerc (Jenna Coleman, The Cry), who may be Sobhraj’s cold-blooded accomplice or his hostage, and the Dutch diplomat, Herman Knippenberg (Billy Howle), who along with his wife, Angela (Ellie Bamber), pieced together Sobhraj’s crimes after local authorities showed little interest.