Pacifica Northwest

 Pacifica Northwest is the most popular girl in Gravity Falls. She comes from a wealthy family, and is the great-great-granddaughter of the supposed founder of Gravity Falls, Nathaniel Northwest (the real founder of Gravity Falls is Quentin Trembly). Pacifica is an unfriendly, sarcastic, spoiled brat and is Mabel's primary rival. Pacifica looks down on Mabel and thinks her eccentric personality is annoying and immature. She uses people's insecurities to manipulate them into doing whatever she wants and despises Mabel for standing up to her.