The secretive military facility Area 51 has inspired its fair share of pop culture, appearing in television shows like The X-Files, and movies like Independence Day. It even sparked a social media resurgence that failed to produce much of a Naruto Run (which is a good thing, considering it is patrolled by armed guards who are, well, armed). However, Area 51 hasn't had such a presence in comics, and it's not hard to see why. After all, why bother with a military base in the middle of the desert when you can have a flying aircraft carrier or an underwater maximum security prison?
Fortunately, Tony Stark did bother. In Avengers #19, Tony reveals that a couple of years earlier, he purchased the sprawling military facility when the government quietly put it on the market. Stark tasked the base with an important mission - hiding the Reality Gem of the Infinity Gauntlet.
That's not to say Area 51 didn't have a couple of previous appearances beforehand. The site was used to contain the powerful In-Betweener before he was freed by America Chavez. If one secretive military installation wasn't enough, there's also an Area 52 in Utah containing various mysteries related to the superhero community. Beyond that, the OG Area 51 has been used by General John Ryker and Gamma Corps in their anti-Hulk operations.
Interestingly enough, it's still in use by the US Hulk Operations as Shadow Base B, as first seen in Immortal Hulk #22. Whether Tony Stark lost ownership of the base by then or somehow shares the base with pre-existing government personnel remains to be seen, though it would seem extremely unlikely Stark would risk the Reality Gem falling into the government's hands. It's possible Stark had lost the artifact by then, as the Reality Gem is presently in the possession of one of Captain Marvel's enemies, Star.
Still, Tony Stark at least partially owning Area 51 makes a great deal of sense. After all, historically, Area 51 was used for testing captured Russian aircraft, giving way to the alien urban legends which captivated pop culture for half a century. It would make the perfect proving ground for Tony's prototype armor, which also could easily be mistaken for an alien spacecraft.
Hopefully, Tony Stark's ownership of Area 51 is more than simply a throw-away line. The setting works as a symbol of Tony's own military-industrial complex, and all the baggage that comes with that messy relationship. Perhaps future comic book creators will build upon this idea. Given Tony Stark's own grandiose and audacious personality, it would be interesting to see just what Iron Man would do with an entire secretive military base at his disposal.