Personas are godly; there's no better way to summarize your research then with a persona. My personas range from detailed to brief and I follow a data-driven approach (Cooper's method) to creating them; however, research is not always possible, and so I create ad-hoc personas that can be created from other exercises like roleplaying, empathy maps, or simple online research. I maintain personas as best as I can throughout the design life-cycle because they are key to ensuring that the design stays focused.