Scarlet Witch Could Be A Villian
This first theory is from a Redditor, so I would highly take this one with a grain of salt. But this one does have some compelling arguments.
So, according to JasonTodd027, supposedly Scarlet Witch was the one responsible for the creation of Ultron. We pretty much meant to believe that in Captain America: Civil War, she was at fault and caused the collapse of the building that eventually led to the Sokovia Accords.
It’s true that Wanda has a lot to be angry about. Her parents died, then her brother was killed in battle while helping the Avengers. And even if she’s not evil at the moment, her sometimes love interest, Vision, is in grave danger, as Thanos will be going after him for the Infinity Stone that powers him.
Looks like we should be keeping an eye on Ms. Maximoff.