Dr. Abigail L. "Abby" Yates is portrayed by Melissa McCarthy in the 2016 film, and is the Ghostbusters' de facto leader.
In the novelization, she transferred to Erin's high school after moving from Indiana in her senior year. The two became fast friends, and spent their college years at the University of Michigan researching ghosts. They collaborated on a book about their findings, but Erin backed out of a planned interview after her graduate advisor at Princeton panned the project. Undaunted, she moved to New York City to continue her research.
In the film, she rereleases her book without Erin's consent, threatening her bid for tenure. When Erin demands to have the book taken down, Abby complies, in exchange for her participation at a ghost investigation with Holtzmann at the Aldridge Mansion Museum. She shares traits to Ray Stantz for both are sometimes get possessed, and they both have the same enthusiasm and talent for invention.