Jon Hamm's Good Omens character Angel Gabriel was originally British

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"Gabriel is barely in the novel," Hamm said, "but he's fleshed out here because Neil Gaiman wanted someone cracking the whip. So he's the guy from head office who is like, 'Hey, what are you doing? Go to work!' As a narrative device it's very funny, and the fact that I get to do it is awesome because originally he was written as British."

Initially, as the actor explained, Archangel Gabriel was imagined as "that stuffy, posh Brit who can't get out of his own way."

But Gaiman soon changed his mind.

"Neil felt he should be from the USA, and that made sense to me," Hamm said. "The idea of the American walking in and saying: 'We gotta do it my way!' is very easy for me to inhabit."

While Gabriel is barely mentioned in the original novel, he was meant to star in Gaiman and Terry Pratchett's long-planned (but unwritten) sequel. So, when it came to adapting the book for TV, Gaiman took that character and slipped him into the story.

"Once we had finished writing Good Omens, back in the dawn of prehistory, Terry Pratchett and I started plotting a sequel," Gaiman explained as he announced Hamm's casting. "There would have been a lot of angels in the sequel. When Good Omens was first published and was snapped up for the first time by Hollywood, Terry and I took joy in introducing our angels into the plot of a movie that was never made.

"So when, almost thirty years later, I started writing Good Omens for TV, one thing I knew was that our angels would have to be in there. The leader of these angels is Gabriel. He is everything that Aziraphale isn't: he's tall, good-looking, charismatic and impeccably dressed."

In the series, Aziraphale (Michael Sheen) reports directly to Gabriel and his angelic executive team, based in a pristine celestial office — a far cry from the (literally) hellish basement Crowley (David Tennant) visits.

However, it seems that that both Heaven and Hell are ultimately eager for the same outcome: Armageddon. Meanwhile, the two field agents decide to band together in an unlikely team in order to protect Earth and prevent the apocalypse.

For Hamm, the story is an analogy for the polarity between the US's Republican and Democrat parties: "We live in a time in which everyone is so convinced that their side is right. But the more you look at it, the more you realise that both sides are ridiculous in their certainty, and that the truth lies in the middle."

The Nice and Accurate Good Omens TV Companion is out now. You can buy it here

Good Omens will be released on Amazon Prime Video globally on Friday 31st May 2019.