The Cigarette-Smoking Man was the mastermind behind many an evil plot on The X-Files, but beyond that, his smoking habit ties him to a larger TV universe. Also known as Carl Gerhard Busch Spender, the always mysterious Cigarette-Smoking Man was usually at the center of most government conspiracy plots uncovered by Mulder and Scully during The X-Files' long run. Despite his clearly advanced age and myriad of health issues, CSM was always a threat, and had an unnatural resistance to dying.
Even now, after The X-Files' season 11 finale saw CSM get shot by Mulder and fall into a river, many assume he's still actually alive, waiting to surface and commit more bad deeds. True to his name though, the one aspect of CSM's character that became most iconic was his constant puffing away on cigarettes. In the case of the ever hard to kill Cigarette-Smoking Man, his brand of choice was Morley Cigarettes, and CGB Spender remained loyal to Morley throughout his storied existence in the X-Files world.
What many X-Files devotees may not be aware of, however, is that the show didn't invent the Morley Cigarettes brand. Instead, Morley dates all the way back to 1960, having first appeared in Alfred Hitchcock's proto-slasher classic The Walking Dead.
As for why the fictional Morley Cigarettes brand - as well as creations like Quentin Tarantino's Red Apple Cigarettes - exists at all, the real-life explanation was initially a desire to avoid offering free advertising to real tobacco companies that had not paid to sponsor a show or movie. Later, as pop culture advertising cigarette brands fell out of favor, Morley was used to allow cigarettes to appear onscreen without being seen as promoting a real brand and meant that shows could get around countries that had laws against advertising tobacco products, such as the United Kingdom. The Morley brand itself was intended as a not very subtle reference to Marlboro - sometimes referred to as "Marleys" in real-life - with onscreen Morley packs looking similar.
The implications of The X-Files being part of a shared TV universe based around Morley Cigarettes become even greater when it is considered that The X-Files is also connected to the enormous Tommy Westphall unofficial TV universe. That theory revolves around the revelation in the finale of 1980s medical drama St. Elsewhere that the entire show and its characters had taken place inside the mind of a young boy. Since St. Elsewhere's characters directly crossed over with other shows, and characters from those shows crossed over with even more shows, some theories posit that an enormous chunk of TV history is set inside Tommy's head. The X-Files connects to Tommy Westphall due to Law & Order franchise character John Munch appearing in a guest role, which would mean all the other shows featuring Morley Cigarettes are theoretically part of the Westphall universe too. It is enough to make any TV lover's head spin.