While the vaguely sinister GLaDOS is the main mascot for the Portal franchise, starting in Portal 2, we received another figure who rose to equal if not greater prominence: Cave Johnson, owner, and CEO of Aperture Science. Cave's bombastic, mildly eccentric mannerisms, bolstered by a fantastic performance from TV and film's J.K. Simmons, led to him becoming a mainstay fixture of the series and one of its most memorable characters (even if there aren't that many characters in this series to begin with).
But how did such an unusual guy get to be the head of a massive, hyper-advanced scientific corporation, and how did he end up losing control of it? Thanks to his numerous prerecorded messages, plus some loose materials left lying around Aperture's bowels, we can piece the story together. Obviously, we'll be getting into major spoilers for Portal 2 here, and that's a game that should really be experienced without foreknowledge, so go play it first.
The Early Years
Aperture was originally founded by Cave in the '40s, though back then, it had nothing to do with science. Aperture started out as Aperture Fixtures, a manufacturer of bathroom shower curtains, though Cave eventually changed the name to Aperture Science Innovators to make his products sound fancier. However, suburban homeowners aren't the only ones who need shower curtains; thanks to his impressive business skills, Cave managed to convince the US military into buying Aperture shower curtains for every single one of their branches (except for the Navy, strangely). This lucrative contract made Cave a very wealthy man, and he quickly put his money to work for him.
After purchasing an abandoned salt mine for a location and hiring the best and brightest researchers and engineers, Cave went to work making the name "Aperture Science Innovators" a little more literal. Aperture was all about unmitigated innovation; if you had an idea (or if Cave had an idea), the lab boys were willing to put it to the test. To ensure ideal results, Cave even managed to hire some peak physical specimens, including athletes, astronauts, and war heroes.
Throughout all of this, Cave also had the caring support of his secretary, Caroline.
The Rough Patch
Unfortunately, Cave was not a scientist by any stretch of the imagination, which means his proposals often resulted in wasted resources and dead test subjects. This was fine for a little while, thanks to Cave's immense wealth, but as the money started to dwindle, it became much harder to maintain testing - not to mention find decent test subjects. By the '70s, Aperture was regularly abducting homeless individuals from city parks and coercing them into testing with cash payments, many of which went unclaimed since the subjects kept dying during testing.
Cave's situation worsened due to a combination of lawsuits stemming from all the aforementioned peak physical specimens that "went missing" after volunteering for Aperture testing and a lack of commercially-viable products. Aperture had plenty of innovation to offer, but they would never release a product until Cave was completely satisfied by it, and by then another research lab like Black Mesa would have already beaten them to the punch.
Cave's Demise
In the '80s, Aperture advanced its own internal technology significantly, employing various forms of automation and robotics around its premises. Unfortunately, these inventions still weren't commercially viable, and so the company ended up on the verge of bankruptcy. In addition to coercing homeless individuals to be test subjects, Aperture employees were required to participate as well. This actually led to an improvement in testing quality since the employees understood how the technology worked, though their extremely unsafe nature meant that many of them still ended up dead.
In a last-ditch effort to create a truly one-of-a-kind product, as well as advance research on the experimental Quantum Tunneling Device (AKA the Portal Gun), Cave spent a large portion of Aperture's remaining coiffeurs on a batch of genuine moon rocks to turn them into a new kind of gel. Unfortunately, the dust from the ground-up moon rocks inflicted Cave with a debilitating illness which, fun fact, is an actual thing that can happen in real life if you breathe the dust from moon rocks.
Realizing he didn't have much time left, Cave ordered his engineers to find a way to map his personality onto a computer, so he could continue to run Aperture after his death. Sadly, they would not complete this research in time, and Cave ultimately succumbed to his illness.
Cave's Legacy
As a contingency plan in case he died before the brain mapping research could be completed, Cave ordered Caroline to take his place as Aperture's overseer. He knew Caroline was just as zealous about science as he was and knew his company would be in good hands. With this appointment, however, also came an obligation to be transformed into an AI, which Caroline submitted to. In the late '90s, this research ultimately came to fruition as GLaDOS came online, but she wound up flying into a homicidal rage, killing a large portion of Aperture's remaining staff with a deadly neurotoxin.
The remaining lab techs began installing personality cores on GLaDOS to suppress her homicidal tendencies, suppressing her original personality in the process. Eventually, though, due to bother GLaDOS's toxin-happy nature and external circumstances related to Black Mesa and a sudden alien invasion, there were no longer any human staff left at Aperture. With the staff dead and GLaDOS's original personality long gone, the name Cave Johnson all but disappeared from its stark white halls.
Infinite Caves
Of course, all of this happened to the Cave Johnson we know. Elsewhere in the multiverse, a completely different Cave running a completely different Aperture Science launched the Perpetual Testing Initiative. Through the use of a multiverse portal, Cave would send test subjects into other Apertures in other universes to try out their testing chambers, then bring them back to Earth Prime so he could plagiarize the designs.
Amusingly, through this process, Cave Prime discovered the existence of another Cave who underwent the brain mapping procedure as originally planned and ended up just as homicidal as GLaDOS. This prompted Cave Prime to immediately scrap the project, realizing that turning people into AIs is a really, really bad idea. If only our Cave had been so lucky. Regardless, while the existence of Cave Johnson was nearly forgotten in the main Portal universe, it's thanks to these infinite Caves that he can still pop up here and there around the franchise, and his voice is always welcomed.