Since I don't know the exact 'el rey based on a true story', I can only guess. It could be that 'el rey' was a historical or contemporary figure. If it's a historical account, it might detail the political, social or cultural environment of the time. For example, if he was a king in a certain era, it could tell about the wars he fought, the alliances he made, and how he influenced the development of his kingdom. It could also explore his personal life, his family, and his beliefs.