After becoming a nun at a young age, Sister Sinister was abducted by aliens who kept her on their ship for 5 years. When she returned to Earth she made it her mission to teach humans about the vastness of the Universe and its inhabitants. This was considered heresy and she was persecuted by the Catholic Church for abandoning her faith. The body modifications that resulted from her abduction proved to be a benefit when it came to self defense, and her superhuman abilities paired with her otherworldly appearance earned her the name Sister Sinister.