Penumbra began as a Swedish first-person survival horror series from Frictional Games, with Penumbra: Overture released in 2007 and followed by Black Plague and Requiem. Its main theme became closely tied to the series' quiet, psychological style of horror, which relied on atmosphere and exploration rather than constant action. Fans later clipped the most memorable section of the theme for reuse online, where its recognisable piano motif works as shorthand for dread. It remains popular because it signals horror instantly without needing a visual jump scare.