There is a world wide catastrophe that is cyclical. There is nothing that can stop it. In the past, because they knew the truth, went to their bunkers. They come out when the world is in chaos and save the day. Setting them up as royalty for the next cycle. Rinse and repeat. This time the evil must be exposed and stopped so the cycle of evil can not get a stranglehold on the population after the reset.
Imagine if he'd started himself on fire. Bet people would believe that too.