In 1921, Zurich-based publisher Rascher Verlag released Psychologische Typen, by Swiss psychiatrist C.G. Jung. The contents of this text introduced new ways of categorizing people and their personality, using four primary functions of consciousness: Sensation, Intuition, Thinking, and Feeling.  Jung believed that all people fell into a combination of these categories and that they predict behavior, or at least better explain it. His model was not the first attempt at deconstructing human thought processes, but it was an impactful one. Jung’s approach led to many breakthroughs, ultimately inspiring some of today’s more recognizable methods, such as the Myers-Briggs MBTI®. As time goes on, new personality models are emerging, including some more scientific alternatives to Jung, and their applications are becoming increasingly specialized.
One example of a specialized framework is the Keirsey-Bartle Unified Model. Presented in 2011 by Bart Stewart, contributor to the game design publication Gamasutra, the model looks specifically at gamers and how they behave in virtual worlds.  It asks the question: given the freedom to act, how do people choose to play? Stewart analyzed a wide variety of existing theories, including the referenced Keirsey (KTS) and Bartle (Player Types), before arriving at his integrated model. As it turns out, there are definite patterns in the way people choose to behave when playing video games and they reflect a few distinct overarching motivators (which we'll introduce below).
While the Keirsey-Bartle Unified Model is intended for understanding video game behavior, it doesn't take a huge leap to begin applying it to other parts of everyday life. In a sense, real life is a game with real-life consequences. If we look at people as active players, gamer or not, can that inform the way we design for them? Can it help us create experiences that invite participation, interaction, and engagement? For those in entertainment, can it help us better understand fan audiences and kickstart new ways of thinking about storytelling?