Barbara is a scientist who provides the Protagonist with a crucial understanding of time inversion early in the film. She is calm, knowledgeable, and precise, explaining the complex physics behind the Tenet system in a way that sets the stage for the Protagonist's mission. Although her role is brief, Barbara’s expertise in the science of entropy and inversion is critical to the Protagonist's ability to navigate the challenges ahead. Her insights into the mechanics of time manipulation make her a key figure in unraveling the film's intricate plot.