Even though it only comes in at around 10 hours total, the two Portal games have been able to spin one of the most interesting gaming narratives that fans still pick apart to this day. The puzzle-based spin-off of Half-Life, the original game was more of an experiment than anything else, a proof of concept for the portal gun that turned out to be way more sophisticated than anybody expected at the time. Over the course of that initial title's tight two hours, players took control of Chel, trapped in a terrifying game of cat and mouse by the rogue A.I. GLaDOS.
Beginning twelve years after Aperture Science's abandonment after the A.I rose up and killed all of the employees, Chel finds herself trapped in the bowels of the facility, forced to complete one puzzle room after another before breaking out of her cage and putting an end to GLaDOS' reign of terror. It's a simple narrative, but the amount of environmental storytelling Valve packed into these intricately-crafted levels hinted towards a wider mythology that screamed to be pieced together.
After a bit of a retcon, the second game picks up with Chel back in the facility, now completely dilapidated. With a new robotic helper in Stephen Merchant's Wheatley, the two accidentally revive GLaDOS during their escape. It turns out she isn't who you should be worrying about though, and it's Wheatley, mad with power, who becomes obsessed with performing tests once he's plugged into the GLaDOS mainframe. Forced to band together to stop a common threat, this time around Chel and GLaDOS form an unlikely alliance, with the latter eventually sparing the former.
Though it's similarly as tight as the original, this time around the game was packed with even more details that fleshed out the history of Aperture Science and its downfall. By visiting labs that were built between the 1960s and 1980s you can find recordings from Cave Johnson, the company's founder, that covers its decline and his death by way of an alleged Moon Dust poisoning. They also shed light on a character called Caroline, Cave's assistant whose personality was used to create GLaDOS in the first place.
The robot is disturbed by this revelation that part of her isn't her, and deletes Caroline's humanity from her programming. While both Wheatley and GLaDOS are clearly positioned as the antagonists of these games, however, one theory does suggest that it's actually Caroline who's the franchise's big bad. Though initially she seems like an innocent bystander in all of the drama - after all, Cave speaks fondly of her and she looked after him when his health began to fail - the implications of some choice audio recordings do cast a sinister light on her character...