 The inspiration for "Fight Club" was a "long-lost nugget" that series creator Chris Carter had thought up a while back. He explained, "I had this idea for a long time to do a story about mis-matched twins that had an almost nuclear reaction when they were around each other." Carter began to write the episode at the same time as the pilot for the X-Files spin-off, The Lone Gunmen. Because of the "insanity" in juggling two scripts at once, many more "crazy" elements made it into "Fight Club". When executive producer Frank Spotnitz first looked at the script, he noted that "[the episode] had an odd tone. It felt like a wild show."
