The line comes from Highlander, the 1986 fantasy action film about immortal swordsmen who duel across centuries for a final Prize. There can be only one was both the rule of their contest and the film's famous tagline, spoken as immortals faced each other knowing only one would survive. The film became a cult hit and spawned sequels and a television series, keeping the phrase in circulation for decades. Online, the clip survived as a soundboard staple for last-man-standing moments because its meaning needs no explanation.