Renowned for his big screen roles in Batman Returns, The Deer Hunter and The Dead Zone, this marks the Oscar-winner's first appearance on British TV, but Merchant always enjoyed the notion of bringing in someone of his “calibre and vintage”.
“I didn't write [the part] specifically with him in mind, but I wrote it with the idea of a sort of American actor of his calibre and vintage in mind,” the Hello Ladies star told Digital Spy and other press.
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“I like the idea of this man who fell to earth, this kind of almost alien presence in Bristol. We're in this provincial world and then in comes this charismatic figure like he's just fallen to earth but ultimately, he's just another petty thief like everybody else.”
Merchant and his team scribbled down a list of potential candidates for the role, on which Walken perched nicely at the top.
“So I went to see him in America, at his house in Connecticut, and someone had said to me before I got there, 'Chris is comfortable with silence.' And sure enough, he's a man who just – he's in his late 70s, he's got nothing to prove to anybody – and he's just quite happy to ask a question and you give an answer and he just muses on it.
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“He said to me, 'What's Bristol like?' And I'm not even joking, I said: 'It's kind of like San Francisco. It has a big bridge, and it's really hilly, and kind of arty,'” recalled Merchant.
“And he just thought about that for what seemed like an eternity. And then I just sat there while he thought about it. Just two men sitting in silence, so the meeting lasted about 4 hours.
“But in the end, I liked him and he seemed to like me, and we got on well, and sure enough, he turned up in Bristol.”
The Outlaws airs on October 25 at 9pm on BBC One.