According to Neil Gaiman, co-author Terry Pratchett's last request to him before his death in 2015 was for Neil to write the screen adaptation. Previous attempts to bring the book to television failed due to not being able to find a writer able to adapt the book while keeping its spirit and humor.
Terry Gilliam tried to adapt this as a movie several times over ten years before admitting defeat. He came closest in January of 2002 when he had Robin Williams on board to play Aziraphale, and Johnny Depp was signed up for the part of Crowley. He had raised fifty million dollars from investors and he just needed a Hollywood studio and a bit more money to start production. His confidence in the project was completely shattered when he found himself in a post 9/11 yet pre-"Pirates of the Caribbean" Hollywood where every studio and producer he met told him the same thing: "nobody wants to see Johnny Depp movies".
Adam's earthly father, Mr. Young, has the license plate number "SID RAT" which spells "TARDIS" backward. The Tardis is the time traveling police box featured throughout Doctor Who (2005), a show in which many of the Good Omens cast has also starred or appeared.
Terry Pratchett famously included several humorous footnotes in most of his novels. Neil Gaiman attempted to include as many of the Good Omens footnotes as possible in the show as Easter eggs. An example is the table tennis set which belongs to the Chattering Order of Saint Beryl.
The demon Crowley takes his name from the English occultist Aleister Crowley (1875-1947). The original Crowley was branded 'The most evil man alive' by the newspaper publisher Max Aitken, 1st Baron Beaverbrook. Crowley conducted rituals to try to produce the Antichrist who he named Moonchild. Jimmy Page, the guitarist of Led Zeppelin fame, was a great fan of Crowley and even bought his former home at Boleskine near Loch Ness.
Neil Gaiman revealed at a panel during New York Comic Con 2018 that the Bentley used in the show is a 1934 model. Neil admitted that no research was done on cars during the writing of the book, so when it came time to select a car for the show they found that the 1929 model mentioned in the book did not have the look that the authors had been going for.
Michael Sheen, playing the angel and book dealer Aziraphale, has said: "I first read Good Omens as a teenager and it's been one of my favorite stories ever since.' Michael Sheen was born in 1969, Good Omens was first published in 1990 - Sheen wasn't a teenager anymore
Madame Tracy lives in the same building as Shadwell, a witch hunter. Miranda Richardson, who plays Madame Tracy, has played a witch on at least two notable occasions: in Tim Burton's "Sleepy Hollow" (1999), and "Harry Potter and the Goblet of Fire" (2005).
Two 'Doctor Who' actors, David Tennant (the 10th Doctor) and Michael Sheen (House, as voice only), star as the leads. Also in this series is Derek Jacobi who played The Master in Doctor Who. Benedict Cumberbatch, who appears as Satan, played Sherlock Holmes in the show Sherlock (2010). Mark Gatiss who acts in this series was also a writer for Doctor Who and co-creator of Sherlock, and appears in both.
"Good Omens" marks the seventh time David Tennant and Nina Sosanya have worked together. Their other titles include "People Like Us - The Actor", "Casanova", "Doctor Who - Fear Her", "Love's Labours Lost", "96 Ways to Say I Love You", and "You, Me, and Him."
In November 2001, when Terry Gilliam was still developing the film adaptation, the Chicago Sun-Times exclusively revealed that Joseph Fiennes and Christopher Lambert would be playing the two angels Crowley and Aziraphale. Soon afterwards, Gaiman's website refuted the item.