Since she was a university student, Katya Adler has been fascinated by the idea of personality - how personalities are formed, how they can change, and whether we even really have a fixed set of characteristics.
For the third and final part of this One to One series about personality, Katya speaks to Wiebke Bleidorn, professor of social and personality psychology and head of the Personality Change Lab at the University of California, Davis.
Wiebke talks to Katya about how the field of personality psychology has evolved, discusses her research into how stable personality traits are and reveals whether it is possible to change someone's personality.
Producer: Camellia Sinclair