The X-Files

In the early years of the series, Mulder is a firm believer in extraterrestrials and Scully is skeptical. In real life this is the opposite, being Duchovny the skeptical and Anderson the believer.

When casting the role of the Cigarette Smoking Man, the producers had no idea the character would turn into a major role in the series. When the character became more prominent, they worried that William B. Davis, who had only been cast as an extra, would not be able to carry the part. As it turned out, Davis, who is one of the most respected acting teachers in Canada, impressed series creator Chris Carter so much that he made the Cigarette Smoking Man the main villain of the series.

During the opening titles, in the Mulder and Scully's FBI ID badges can be read "Federal Bureau of Justice, United States Department of Investigation." This alteration was necessary as making a fake FBI badge, even for fictional purposes, is illegal. The real-life quote is: "Federal Bureau of Investigation, United States Department of Justice."