Why Wanda became the Scarlet Witch
Jimmy Woo emphasized WandaVision Wanda didn’t even have a fun superhero title. Viewers know her as the Scarlet Witch, but she was never called on screen until the end of Episode 8 after Agatha got the full picture of her powers.
Usually portrayed as a mutant, like X-Men, she started out as a superhero alongside her brother, Quicksilver, but then switched sides to join the Avengers. At one point, she had a magical twin, and it turns out that these sons are part of Satan, thanks to the supernatural demon Mephisto. In later comics, she is no longer a mutant but a witch born.
In the MCU, Scarlet Witch appears to be more of a concept than a specific person, at least based on the way Agatha Wanda has given it the title. Wanda had witch visions when she first touched the Mind Stone during the HYDRA experiments, and Agatha gave her the name after learning how Wanda created her sitcom world and made the vision completely distant from magic.