Left 4 Dead is a cooperative first-person shooter released by Valve in 2008, followed by Left 4 Dead 2 in 2009. Its campaigns use dynamic music and audio cues to warn players about hordes, special infected and nearby threats, with the game's AI Director changing intensity based on how the team is performing. That adaptive sound design became a defining part of the series, and short scary cues were later clipped for soundboards, edits and memes. Players who know the games recognise the tension immediately, even outside the original context.