It's pretty tough to design a great user experience if you don't know the target audience. So when faced with this problem, well-equipped UX designers will turn to one of their favourite tools: the persona.
Personas draw upon the power of narrative and storytelling to shine a bright light on the elusive "user." They're especially effective when based upon primary research methods such as ethnography and in-context interviews. Done poorly, personas are little more
than a futile exercise in creative writing. But done properly, they become powerful representations of your users’ goals, motivations, and behaviours -- and can act as the "north star" for your design decisions.
From my guest lecture at Conestoga College in Kitchener, Ontario, Canada on September 27, 2013.