The real-life Gary Johnson passed away early on in production and never got to see the film. Richard Linklater only talked to him on the phone, and never got to meet him in person.
The script originally had the story taking place in Houston, since the real-life Gary Johnson was based in Houston, but due to Texas tax credits and other financial elements, they weren't able to shoot the film in Texas, and instead chose to set the film in New Orleans.
The teenager giving Johnson video games to kill his Mom is based on an actual client meeting the real life Gary Johnson had. A Houston teenager named Shawn Quinn, a brilliant kid with an IQ of 131, gave Johnson seven Atari computer games, three dollar bills, and $2.30 in nickels and dimes to kill a male classmate he thought was trying to win the affection of a girl he liked.
This movie is based on a longform narrative article by Skip Hollandsworth, published in Texas Monthly in October 2001. This marks the second time that Linklater has made a movie based on a Texas Monthly article by Hollandsworth, the first time being Bernie (2011).
One of the personas Gary Johnson (Glen Powell) plays when meeting a client is based on the character Patrick Bateman (Christian Bale) in the film American Psycho (2000).