In most cases, 'El Rey' is not based on actual events. It's more of a fictional narrative crafted for entertainment purposes. The plot and characters might be inspired by various elements but not by real-life happenings.
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.
If 'el rey based on a true story' is about a person's rise to power, you might like 'The Social Network' which is also based on a true story about Mark Zuckerberg and the founding of Facebook. Another one could be 'The Imitation Game' which tells the story of Alan Turing.