It was Daniel Craig's performance in this movie that caused producer Barbara Broccoli to take notice and think he might be a good fit for James Bond.
When Gene gives XXXX a handgun, producer and director Matthew Vaughn said on the DVD commentary on that scene that Daniel Craig's character "wants to be James Bond." Craig would be cast as James Bond in Casino Royale (2006) and his co-star, Ben Whishaw, would appear in future Bond films with Craig.
In the opening montage, XXXX walks through a pharmacy, in which he imagines all of the products are drugs, like cocaine and ecstasy, branded with labels such as "FCUK reality." The founder of French Connection (FCUK), Stephen Marks, was the executive producer of this movie.
"Layer Cake" author J.J. Connolly designated his protagonist as "XXXX" in his mind until he could think of a suitable name for the character. Ultimately, he decided that the character didn't need a name for the story to be effective.