The X-Files became a landmark show in the 1990s for a lot of reasons. First of all, the concept was incredibly intriguing and original. The idea of FBI agents investigating things like aliens and urban legends was unlike anything that came before it and allowed for wildly different kinds of episodes every week, from sci-fi to horror to even the occasional comedy.

Lead actors David Duchovny and Gillian Anderson deserve a great deal of credit too, as both of them were engaging in their contrasting roles, with Mulder as a true believer in the paranormal and Scully as a scientific skeptic. Their chemistry onscreen was also undeniable.

None of it, though, would have worked without the excellent writing. Chris Carter, Frank Spotnitz, Darin Morgan, John Shiban, and several others wrote incredible scripts for Mulder, Scully, and the foray of guest stars and recurring characters. (Though there was the occasional bad episode thanks, in large part, to the rigorous demands of network TV back in the 1990s).

One particularly great episode titled “One Breath” arrived during season 2. In it, Agent Mulder is searching for Agent Scully, who has been missing for several episodes after being kidnapped by an alien named Duane Barry (Steve Railsback).

The episode was written by Glen Morgan and James Wong, formative writers on the series for the first two seasons. After creator Chris Carter wrote the first two episodes, which introduced Mulder and Scully, and laid the groundwork for the show’s overall conspiracy story, Morgan and Wong wrote episode 3, “Squeeze,” which was the show’s first “monster of the week” story. In an interview with Cracked, Breaking Bad creator Vince Gilligan, who got his start on The X-Files, praised the duo of Morgan and Wong, saying, “I tend to think that Glen Morgan and Jim Wong don’t get enough credit. They had some killer lines between Mulder and Scully in certain early episodes.” Gilligan was referring to their comedic chops, but it holds true of all of their work on the series. Glen Morgan and James Wong were a huge influence on The X-Files during its most formative years and delivered some especially sharp dialogue.

This is why, for X-Files aficionados, it shouldn't be surprising that they were the writers of the episode that contains the show’s best-ever quote. (I assume they also wrote the line, but TV writing is very collaborative, so it's tough to be sure.)

The line comes after Scully is returned, when Mulder finds out the whereabouts of the Cigarette Smoking Man (William B. Davis). In the scene, Mulder points a gun in the Smoking Man’s face and demands to know why Scully was targeted. Shouting, Mulder says, “You’re going to answer me, you son of a bitch!”

In response, the Smoking Man coolly utters the single greatest line in the history of the series.

“Don’t try and threaten me, Mulder. I’ve watched presidents die.”

He then proceeds to light another cigarette.

Don’t try and threaten me, Mulder. I’ve watched presidents die.

First of all, the line is just badass. The Smoking Man was always an intriguing character in the series, in large part because of the cool detachment Davis brought to the role. This particular line, and the way in which it was delivered, show so much about the character. You cannot phase him. He’s seen it all and has been present for, or perhaps caused, some of the worst events in American history (in the season 4 episode “Musings of a Cigarette Smoking Man,” it's implied that the Smoking Man may have, indeed, killed JFK). The casual nature of the boast is chilling, and the fact that he lights another cigarette simply underlines how unfazed he is to have a gun in his face.

The line also points at something larger about The X-Files overall. The show’s biggest story was always about Mulder’s search for the truth about the biggest secrets being kept from the American public. “The truth is out there” is the series’ biggest refrain, included during the show’s opening credits. Mulder, thanks to his long-running crusade for the truth since his sister was abducted by aliens when he was a child, represents the truth and the pursuit of it.

But if Mulder represents the truth, surely, the character who represents the lie is the Smoking Man. He was the show’s longest-running villain and was a central figure in the countless lies kept from the American people. That’s what makes his line, “Don’t try and threaten me, Mulder. I’ve watched presidents die,” the best, sharpest, most telling line in the entire 11-season run of the series.