"Every cast of characters has at least one primary persona. The primary persona is the individual who is the main focus of the design. To be a primary, a persona is someone who must be satisfied, but who cannot be satisfied with an interface designed for any other person."
Alan Cooper, The Inmates are Running the Asylum
"The goal is to find a single persona from the set whose needs and goals can be completely and happily satisfied by a single interface without disenfranchising any of the other personas."
Alan Cooper, About Face 2.0