Taking this one step further, it’s plausible Plaza is playing her. There’s no Rio Vidal in the comics, and given the MCU’s reputation for reinventing classic characters, the name might be a cover for her true identity. After all, Death has previously merged with the mortal Marlo Chandler and used her alias in the past. We know Rio’s backstory makes her an old enemy of Agatha (Kathryn Hahn), but the latter can’t kill her. Even though this could have something to do with a blood pact or how Agatha got her hands on the Darkhold, what if Harkness can’t kill “Rio” because she’s the literal embodiment of Death?
First introduced in 1973’s Captain Marvel #26, Death is the embodiment of life ending as the opposite of the cosmic entity known as Eternity and is typically confined to the Realm of the Dead. She originally featured as part of Thanos’ convoluted scheme to conquer the universe and court her after destroying all life. Although Death is impressed that Thanos takes control of the universe with the Cosmic Cube, she later abandons him when Captain Marvel, Drax the Destroyer, and the Avengers defeat him. Death most famously appears during “The Infinity Gauntlet” arc, where the Mad Titan tried to collect the Infinity Gems and perform his (now-infamous) snap.
This wouldn’t be Death’s first wink in the MCU. As far back as 2012’s The Avengers, there was a throwaway mention about how challenging it is for humans to ‘court’ Death. The temple walls on Morag featured a mural of the Infinity Stones and Death alongside the entities of Entropy, Infinity, Death, and Eternity in Guardians of the Galaxy, while Thor: Love and Thunder again featured a statue of Death. Joss Whedon admitted to IGN in 2018 that his Death tease at the end of The Avengers was there as a placeholder, and although he wasn’t sure the character would translate, he went on to praise the Russo Brothers for omitting her from Avengers: Infinity War and Avengers: Endgame.
Still, the Russos thought about sticking closer to the comics by having Death as the reason Thanos sought the Infinity Stones in the MCU. Speaking to Business Insider, Anthony Russo explained how we only had two-and-a-half hours with these characters without introducing a new one and their convoluted backstory. Joe Russo added, “The big-screen Thanos still aspires to kill off half the universe, but this time around, he merely wants to solve an overpopulation crisis instead of using mass murder as foreplay.” She’s still acknowledged in some form, as Red Skull actor Ross Marquand later confirmed to a panel at the Edmonton Expo (via @AgentsFandom) how his cloaked appearance was a nod to Death in “The Infinity Gauntlet.”
Note: The rest of this article contains information about merchandise leaks that will almost certainly spoil the identity of several Agatha All Along characters. Avoid reading if you don’t wish to know.
Rumors are swirling that Agatha All Along is setting Rio up for her own twist akin to WandaVision’s “It was Agatha all along”, and if you still aren’t sold, a leaked Funko! Pop vinyl (via ComicBoomMovie.com) apparently confirms she’s indeed playing Death. The reveal has seemingly been under our nose all along, and looking back at some tarot-inspired promo art, you’ll spot that the “Death” card has a hooded skeleton clearly holding the knife that Rio attacked Agatha with in episode 1. Going three for three, a September 20 promo featured the coven using an Ouija board that spells out “Death”.
