The one thing you can always count on in the Marvel Cinematic Universe is that nothing happens on accident. Any scribble on the wall or throwaway line has meaning, which is why when Monica Rambeau said she was going to call an "aerospace engineer" to come help SWORD investigate the Hex, fans immediately took notice. The mysterious aerospace engineer on WandaVision should hopefully be coming to the show soon, and you bet there are already theories about who it will be. Spoilers for WandaVision Episode 5 ahead.

Before we get into the theories, though, it's important to remember the earth-shattering twist in Episode 5, "On a Very Special Episode..." In the same episode that Monica mentioned this "aerospace engineer" she knows, WandaVision officially opened up the multiverse when Evan Peters' Quicksilver, previously seen in Fox's X-Men films, showed up as Wanda's brother, Pietro. On any other show, I might say that this could just be some clever stunt casting, but this is Marvel we're talking about. There's no question about it: the multiverse is happening, and that means that Monica's aerospace engineer friend could be pretty much anyone in known Marvel canon.

Whoever this aerospace engineer is, they have to fall into one of these two categories: either they're a returning character from the MCU, or they're brand new to the Marvel universe. So, either a fan-favorite is about to cameo on WandaVision, or the Disney+ show will introduce a new character to the MCU. Here are the fandom's best guesses.