The truth is out there — or so we were told when The X-Files first introduced itself to the world 20 years ago today.

That tagline has outlived the series that spawned it, taking its place as a permanent part of the pop-culture lexicon — a testament to the success of a series that ran for nine seasons before departing the airwaves in 2001.

The X-Files wasn't exactly an instant hit. Its opening episode was watched by just 12 million people, a number that would constitute a massive hit today, but was unspectacular for its era. The show's highest-rated moment came in 1997, when Fox aired the fourth season's "Leonard Betts" episode immediately after Super Bowl XXXI.

Since its run, The X-Files' influence has stretched far beyond the audience that originally consumed the show. In fact, without The X-Files, we might never have had Lost, Breaking Bad, Game of Thrones, or many of the other staples of the so-called "golden age of television" we're still enjoying today.

Sci-fi and fantasy are big business in television now — but when The X-Files premiered in 1993, betting on the genre was widely regarded as a major gamble by Fox. The 1990s was a time when the sitcom was king, when shows like SeaQuest DSV and Walker, Texas Ranger were what passed as "creative" network programming. The X-Files proved an unexpected hit with the coveted 18-49 demographic — which made it an unexpected hit with advertisers. Suddenly, the "cult" was mainstream, hitting magazine covers and movie theaters — and the other networks couldn't help but notice the money their competitor was raking in.

The form The X-Files took was just as important as its content. The series unleashed a bevy of overarching storylines: What happened to Mulder's sister? What was the Cigarette Smoking Man's real goal? Would Mulder and Scully ever act on that sky-high sexual tension? Audiences' obsessive engagement with these questions offered proof that we were ready for season-spanning storylines, complex mythologies, and ever-darker subject matter. It's for good reason The X-Files was one of the first shows to make entire seasons available for purchase on DVD — a practice that has since migrated to Netflix.

The X-Files set the stage for episodic enigmas like Lost, freak-of-the-week staples like Supernatural, and horror/humor like Buffy the Vampire Slayer — which Joss Whedon once described as "My So-Called Life meets The X-Files." But it also offered a training ground for some of today's top TV talent. Homeland co-creators Howard Gordon and Alex Gansa both cut their teeth in The X-Files writers' room, and it's easy to find embryonic origins of their Emmy-winning drama in X-Files episodes like "Sleepless" and "Unrequited" — both of which involve soldiers struggling to reintegrate into everyday life after returning from active duty. Other key X-Files alumni include Darin Morgan (Fringe), David Amann (Castle), John Shiban (Hell on Wheels), Greg Walker (Vegas), and Vince Gilligan (Breaking Bad), who got his big break after sending in a speculative script as a fan during The X-Files' second season.

As with any show that's two decades old, there are aspects of The X-Files that haven't aged well — but for anyone who hasn't experienced its influence firsthand, the barrier to entry has never been lower. (All nine seasons are available to stream on Netflix). And even as The X-Files finds its legacy overshadowed by many of the other shows out there, the truth — if it is indeed out there — will lead critics and audiences alike to recognize The X-Files' pivotal place in TV history.