Jon Hamm will be God’s messenger in “Good Omens,” Amazon and the BBC’s adaptation of the Terry Pratchett and Neil Gaiman novel.

Hamm (“Baby Driver”) has been cast as archangel Gabriel, the primary messenger of God, in the upcoming six-part series, which has just gone into production.

The “Mad Men” star professed to being a fan of the original novel, but thought it could never be filmed. “I read ‘Good Omens’ almost 20 years ago,” he said. “I thought it was one of the funniest, coolest books I’d ever read. It was also, obviously, unfilmable. Two months ago Neil sent me the scripts, and I knew I had to be in it.”

Hamm’s character has a fleeting role in the book, but Gabriel has been worked up for the series. “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,” said Gaiman, who penned the series and is showrunner on the project. “So when, almost 30 years later, I started writing ‘Good Omens’ for TV, one thing I knew was that our angels would have to be in there.”

Hamm joins a lineup that includes Michael Sheen and David Tennant in the lead roles of the angel Aziraphale and the demon Crowley, respectively. Jack Whitehall, Michael McKean, Miranda Richardson, and Adria Arjona are also among the cast.

Gaiman expanded on the Gabriel character in the series. “He is everything that Aziraphale isn’t,” he said. “He’s tall, good-looking, charismatic and impeccably dressed. We were fortunate that Jon Hamm was available, given that he is already all of these things without even having to act.”

BBC Studios, the production arm of U.K. pubcaster BBC, is producing “Good Omens.” It will bow on the Amazon Prime Video streaming service in 2019, and then run on BBC Two in the U.K.