The phrase "Damon Salvatore rule" originates from a joke within the 'The Vampire Diaries' fan community, but its meaning evolved from a somewhat niche idea into a shorthand for a broader, recognizable character type.
It began as a Tumblr or forum post—I wish I could find the original, but it's been lost to time. The idea was simple: no matter how objectively toxic or problematic a character's actions are within a story, if they are portrayed by an actor with a specific kind of charisma and vulnerability, a significant portion of the audience will not only forgive them but fervently defend them. Damon, as played by Ian Somerhalder, was the perfect case study—introduced as a murderous, manipulative antagonist, yet his complexity and the actor's performance sparked a massive fan following that often eclipsed that for the more traditionally heroic brother, Stefan.
The "rule" then got applied to other characters in similar shows or books, like Klaus Mikaelson from 'The Originals' or even book counterparts like Warner from 'Shatter Me'. It speaks to a viewer/reader priority on emotional resonance and compelling performance over strict moral alignment. It's less an actual rule and more an observation about how fandom engagement works, where a character's journey and presentation can completely override their in-universe moral ledger.
Now, you'll see it referenced in discussions about any 'dark' or antihero lead, especially in paranormal romance or urban fantasy, where fans debate whether their love for a character is about the writing or the performative charm layered on top. It's fascinating how a fandom in-joke can crystallize a whole dynamic of audience reception.