Reavers are fictional characters from the Firefly universe, created by Joss Whedon. They are depicted as violent and savage humans who have lost their sanity due to exposure to a mind-altering substance called Pax. This substance was intended to pacify the population of the planet Miranda, but instead led to the creation of the Reavers, who now roam space in their ships, attacking and terrorizing other travelers. In the Firefly series and its follow-up film, Serenity, Reavers are portrayed as a significant threat to the main characters. Their brutal nature and unpredictable behavior make them one of the most feared groups in the galaxy, often leaving destruction in their wake.