Committed to a fully developed back story, director Tony Gilroy spent a good deal of time establishing the details of "Realm and Conquest" with production designer Kevin Thompson. The director explains that right from the beginning, when he first read the script, he could tell that "Realm and Conquest" was going to be a key prop. In the movie it's a metaphor for truth and justice. In creating the details of the fictional novel, Thompson generated original visuals inspired by German Expressionistic images cut from wood blocks, and Gilroy wrote the first two pages for three chapters of the book. They even went as far as designing a "Realm and Conquest" card game for a scene between Henry and Michael. Thompson offers, "This detail was important to Tony because, in his own life, novels and games similar to 'Realm and Conquest' allow him to connect with his son in a meaningful way."
The film's director Tony Gilroy grew up about 65 miles north of New York City in Orange County, New York and did not forget where he came from in his directorial debut. It is mentioned that Michael Clayton attended Washingtonville Central High School; graduating in 1977. Gilroy, himself, graduated from Washingtonville High School in 1974. The home of Michael Clayton depicted in the film is actually in Blooming Grove, NY. The airport where Michael boards a private jet was filmed at Stewart International Airport in New Windsor/Newburgh, NY. And the pivotal moment of the film involving an incident with a main character's automobile was filmed at the Moodna Viaduct in Salisbury Mills, NY. All of these locales are within 7 miles of his hometown.
During a scene were Edens is wandering through Times Square, a U-North advertisement appears on a massive video screen. Beneath the screen on the side of a bus is another advertisement for a musical called Wicked. While Wicked is about the witches of Oz, its appearance in the same shot as the name of the company Edens was defending is appropriately coincidental given the plot of the movie.
George Clooney, Tilda Swinton, and Tom Wilkinson have all been in comic book movies. George Clooney played Bruce Wayne/Batman in Batman & Robin (1997), Tilda Swinton played the Ancient One in Doctor Strange (2016), and Tom Wilkinson played Carmine Falcone in Batman Begins (2005), making him and Clooney related to the same media.
The trivia item below may give away important plot points.
The Mercedes-Benz S-Class sedan that is blown up in this film was first used in filming of The Devil Wears Prada (2006). For the earlier film it was cut in two for use in process shots featuring Meryl Streep and Anne Hathaway. It was then welded back together and repainted in order to be blown up in Michael Clayton (2007). The car's preparation was featured on Shooting Cars (2006).