Agatha Harkness is a watch from WandaVision. She was the villain of the story.
She was accused of practicing dark magic by her own coven during the Salem Witch Trials. Her own mother tired but failed to kill her.
In the 20th century, she went to Westview, where she sensed chaotic magic made by Wanda. She lived as Wanda's neighbor and all the while interfering with Maximoff's idyllic paradise to her own benefit. After discovering that Maximoff was Scarlet Witch, Harkness was defeated and stripped of her magical abilities, indefinitely condemned to live out her life as Agnes in Westview.