The Red Death is the overarching antagonist of the How to Train Your Dragon franchise, serving as the main antagonist of the 2010 animated feature film How to Train Your Dragon, a major antagonist in Dragons: Rise of Berk and School of Dragons, and a posthumous antagonist in the rest of the franchise.
They are the reason for the three hundred year war between the humans and the dragons. Fortunately, The Red Death was defeated by Hiccup and Toothless and ended the three hundred year war between humans and dragons.
The Red Death is also the only main antagonist in the franchise to be a dragon while the other films and television had humans as villains. They are based on the Green Death from the original book, How to Train Your Dragon by Cressida Cowell.