We can't quite talk about WandaVision without considering the Scarlet Witch's origins in the ever-expanding Marvel Cinematic Universe. And, of course, we can't dive into Elizabeth Olsen's Wanda Maximoff without mentioning her twin brother Pietro Maximoff (Aaron Taylor-Johnson), aka Quicksilver. While Wanda has been a mainstay character in a handful of Avenger movies, we haven't seen her brother as much. The short and simple reason why is that Wanda's twin dies soon after his first appearance, when the Avengers battle Ultron. Need a refresher on what happens to Pietro before diving into WandaVision? Here's a quick rundown of his role in the MCU thus far.
We first see the Maximoff twins in Captain America: The Winter Soldier during a mid-credits scene where Baron Wolfgang von Strucker experiments with the siblings. Avengers: Age of Ultron opens with the Avengers infiltrating the Sokovian HYDRA facility where Strucker conducts tests on his subjects with a scepter previously held by Loki. Here, we officially meet Pietro and Wanda Maximoff, aka Quicksilver and Scarlet Witch. Quicksilver possesses superhuman speed while his sister wields telekinetic powers — and more. Tony Stark ultimately uses the scepter to activate his Ultron global defense program. However, there's a hitch in his plan: Ultron becomes a sentient being who destroys J.A.R.V.I.S. and attacks the Avengers. After escaping, Ultron retrieves a synthetic body and builds an army of robot drones.
At first, Pietro and Wanda are down to join Ultron because they blame Tony's weapons for their parents' deaths. However, Wanda is able to read Ultron's mind and discovers that he wants to save the Earth by literally destroying humanity. Long story short, Pietro and Wanda help the Avengers when they return to Sokovia, where Ultron builds a machine to lift a chunk of the capital and crash it downwards to eliminate humans. During a battle against Ultron's army, Pietro shields Clint Barton, aka Hawkeye, from gunfire and swiftly dies after this final sacrifice. A heartbroken Scarlet Witch grows vengeful and destroys Ultron's body by ripping out his core processor, which, unfortunately, triggers the machine. Thankfully, Tony and Thor are able to break up the landmass and save the world. (Vision actually saves Wanda during this ordeal.) After her twin's tragic death, Wanda joins the Avengers.
Will we see Wanda's brother in these coming episodes of WandaVision? Perhaps. It's clear that something is awry with Wanda's world, and both she and Vision don't quite know their own history. Since Vision is dead and has managed to somehow come back, we may very well see Pietro, even if only in a hallucination or flashback.