This voice line comes from the Warhammer 40,000 strategy game Dawn of War, where Imperial Guard soldiers, known as Guardsmen, call out enemy units they encounter on the battlefield. Their alarmed reports became a familiar part of the game's soundscape for players, and short clips later spread through soundboards and gaming videos as shorthand for spotting something powerful or out of place. It endures because the contrast between an ordinary soldier and a Space Marine is instantly funny and dramatic.