The show was always vague about who he was -- his name may have been Spender, he may have been Mulder's father, and he may have killed JFK, but all we know for sure is that he was one evil dude. You can tell from the cigarette.
Why We Almost Didn't Get Him:
It's true that he was there from the beginning -- the Smoking Man appeared in the first scene of the pilot episode -- but he didn't appear again until the last scene of the Season 1 finale. In neither scene does he have a speaking role. That's some ominous-as-shit foreshadowing!
That's why we've shivered at every job interview since '93.
Except that it wasn't. The Smoking Man was an extra, known in the script only as, you know, "the Smoking Man." His entire purpose was just to stand around in the background whenever the writers wanted to remind the audience that Mulder and Scully were being watched by somebody. If you don't know what we mean, go look at the IMDb page of the actor, William B. Davis. Before his 1993 casting in The X-Files, he was playing roles that didn't even get actual names -- he played "Judge" in an episode of MacGuyver, "Doctor" in one episode of Nightmare Cafe, and "Lawyer" in the TV movie Omen IV: The Awakening. And who could forget his work as "Inspector #2" in that one episode of Wiseguy?
So why would the producers of The X-Files declare this random background actor to be the central villain of the show's overarching storyline involving alien beings, government coverups, and unresolved subplots? They even did an entire episode joking that Cigarette Smoking Man was behind pretty much every terrible world event of the last 40 years. The answer is that the writers never intended for that to happen at all.
Another conspiracy sadly debunked.