Mr. Robot hasn't made mention of Elliot's third personality since the Oct. 13 episode, when a flashback showed him and his mother waiting for "the other one." Needless to say, the lack of further information has only intensified speculation, and the latest fan theory suggests "the other one" has been been hiding in plain sight this whole time.

Most theories so far have revolved around the third personality being a character viewers have already met and spent plenty of time with — someone like Tyrell Wellick or Whiterose. But these scenarios strain credulity and would require lengthy explanations; we've seen Elliot interact with these people, we've seen these people interact with other characters, and we've seen Elliot and these people interact while other people are in the room. How would Elliot have had a double life being married to Joanna Wellick and fathering a son without anyone knowing?

Instead, this new theory — which actually finds its basis in a theory that's been around for several seasons — posits that Elliot's third personality has gone unnoticed until now because he looks exactly like Elliot's second personality. Could Christian Slater have been playing two characters this whole time without anyone catching on? Could the figure whom viewers know as "Mr. Robot" actually be two distinctly separate manifestations of Elliot's mind? If so, how would you tell them apart?

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Four seasons in, you may have noticed that sometimes Mr. Robot is seen with his hat, and sometimes without. On a show where every clock face, hallucination, and dream sequence means something, surely the choice of when Mr. Robot wears his most iconic accessory and when he doesn't can't be arbitrary.

Sure enough, some eagle-eyed fans think they've spotted a pattern regarding Mr. Robot's headwear. A year ago, before viewers even knew about the existence of a third personality, Reddit user thatburgerdan noticed that Mr. Robot appeared to behave in subtly different ways depending on if he was wearing his hat in the scene or not. A month ago, Reddit user vascopatricio combined this old theory with the current quest to uncover the identity of "the other one," meticulously tracking every instance of Mr. Robot wearing a hat (or not) on a re-watch of the series.

The results are fascinating. Consistently, Mr. Robot appears more aggressive and violent when wearing the hat, and more calm and protective when not wearing the hat. The hat-wearing Mr. Robot is the one who seriously injured Elliot by pushing him onto the rocks at Coney Island, who threatened Romero with a gun, and who intimidated Krista during a therapy session. The non-hat-wearing Mr. Robot is the one who stayed by Elliot's side when he was suffering through withdrawal in Season 1, who consoled Elliot during his prison beating in Season 2, and who balked at the idea of manipulating Olivia in Season 4.

Scott McDermott/USA Network

What if Mr. Robot doesn't just have wild mood swings — sometimes benevolent, sometimes aggressive — but is actually two completely different characters, only nobody noticed this whole time because they're both played by Christian Slater? Perhaps Elliot has two alters with the same face, a demon and an angel. One we can refer to as "Edward Alderson," modeled accurately off Elliot's real-life father, who viewers just learned was actually a predator who abused his son throughout his life; and one we can refer to as "Mr. Robot," Elliot's idealized version of what his father should have been: caring, helpful, protective.

This could also answer the question of what Elliot was referring to when he, as Mr. Robot (or Edward?), told Tyrell in Season 2, "You're not seeing what's above you." What is above him? Viewers assumed Elliot was referring to something metaphorical, some larger goal or big picture Tyrell was failing to see. But what if he was literally talking about the hat on top of his head, as vascopatricio theorizes? Who knew that a piece of clothing could be the key to unlocking Elliot's mind?

Still not convinced? Watch the below interview of Christian Slater on Jimmy Kimmel Live! in September of this year, shortly before the fourth and final season premiered. In the middle of a lighthearted, jocular conversation about his character's iconic hat, Slater dropped in a telling statement, which can be heard at the 5:37 mark: "That's what the whole fourth season — I'll let you in — it's all about the hat." After the audience laughed and applauded, Slater shrugged. "I'm in so much trouble now," he said.

In the midst of all the good-natured joking, this seemingly innocuous statement slipped by virtually unnoticed; Kimmel immediately launched into asking Slater about building a character around an object or a piece of clothing, and Slater's "spoiler" was never mentioned again. But what if he wasn't joking? What if he did actually reveal the key to unlocking Mr. Robot in the middle of this random late-night interview, and nobody noticed?

If it's revealed in the weeks ahead that Slater has been playing two characters this whole time, that will go down in history as one of the most well-executed television twists of all time. It will also make Mr. Robot as a show that you have to start watching again immediately. Every single interaction Elliot has with his alter will have to be reexamined with this new context in mind.

After four seasons, viewers are finally starting to see what's above them — and it looks a lot like Mr. Robot's hat.