Sans is the final boss of the Genocide Route in Undertale, released in 2015 by Toby Fox. His fight became famous because his very first attack breaks the game's usual mercy, catching players who expected a slow opening turn. Clips of that opening spread through YouTube, fan games and meme edits, turning the sound into shorthand for a deceptively powerful opponent. It remains popular because the attack is instantly recognisable to Undertale fans and still reads as sudden danger even to viewers who have never played the fight.