WARNING: The following contains spoilers for WandaVision Episode 9, "The Series Finale," streaming now on Disney+.
For weeks, WandaVision has kept viewers guessing whether Evan Peters' Pietro, aka Fake Pietro or "Fietro," is the Quicksilver from Fox's X-Men movie universe, secretly the devilish Mephisto, or merely an ordinary resident of the Marvel Cinematic Universe who was roped into Agatha Harkness' scheme. The Disney+ series finally provided the answer to that question in the aptly titled "The Series Finale," revealing that Fietro is none other than Agnes/Agatha's frequently referenced "husband" Ralph.
It was Monica Rambeau who discovers the truth about "Fietro." Following their brief encounter during the Episode 7 post-credits scene, Monica confronts Fietro -- in what she believes to be Agnes' attic -- about his true identity, before promptly uncovering a photo that identifies him as Ralph Bohner. Putting two and two together, Monica realizes the house actually belongs to Fietro, who, in keeping with his established personality, laughs at hearing Monica say his own last name. In a scuffle, she's able to remove the necklace that permitted Agatha to control Ralph.
As much as some viewers were understandably hoping Fietro would turn out to be Quicksilver from another Marvel universe (be it Fox's X-Men franchise or otherwise), this reveal is in keeping with everything else WandaVision did throughout Season 1. Easily the most postmodern MCU project so far, the series was all about taking audiences' expectations and flipping them on their head. In the case of Fietro, the show cast Peters as a way of misleading viewers into presuming the character would have to be connected to his X-Men superhero, as opposed to the unseen Ralph who was so frequently the butt of Agnes' jokes. Indeed, it seems the whole point was to leave viewers wondering whether they could take Peters' casting at face value, much like the characters on WandaVision were often left wondering what was and wasn't real.
From a storytelling perspective, it's arguably better that WandaVision didn't dive fully into the multiverse by bringing back Peters' Quicksilver. The existence of other Marvel universes is a massive topic, enough so that it might have distracted from the show's nuanced exploration of Wanda's grief and how she gradually learns to come back to reality after everything she's lost, as painful as it is. Instead, WandaVision wound up exploring the idea of "alternate realities" in a more figurative sense, portraying TV sitcoms as coping mechanisms, while at the same time acknowledging that comfort television (like all art) is limited in terms of its therapeutic value.
It's also worth pointing out that Peters playing Ralph on WandaVision doesn't mean other upcoming MCU projects are going to use similar fake-out castings to mess with audiences.
Reports of multiple villain actors from Sony's non-MCU Spider-Man movies joining the cast of Spider-Man: No Way Home, along with Spider-Man trilogy veteran Tobey Maguire and The Amazing Spider-Man's Andrew Garfield, suggests the sequel will wind up exploring some type of multiverse storyline in the build-up to 2022's Doctor Strange in the Multiverse of Madness. Benedict Cumberbatch is likewise set to return as Stephen Strange in No Way Home before his next solo adventure, so it's only a matter before the MCU gets into the multiverse proper.
Written by Jac Schaeffer and directed by Matt Shakman, WandaVision stars Elizabeth Olsen as Wanda Maximoff/Scarlet Witch, Paul Bettany as Vision, Randall Park as Agent Jimmy Woo, Kat Dennings as Darcy Lewis, Teyonah Parris as Monica Rambeau and Kathryn Hahn as Agnes. The series is now streaming on Disney+.