The X-Files is an American science fiction horror drama television series created by Chris Carter. The program originally aired from September 10, 1993 to May 19, 2002 , spanning nine seasons and 202 episodes. The series revolves around FBI Special Agents Fox Mulder (David Duchovny) and Dana Scully (Gillian Anderson) investigating X-Files: marginalized, unsolved cases involving paranormal phenomena. Mulder believes in the existence of aliens and the paranormal while Scully, a skeptic, is assigned to make scientific analyses of Mulder's discoveries to debunk his work and thus return him to mainstream cases. Early in the series, both agents become pawns in a larger conflict and come to trust only each other. They develop a close relationship, which begins as a platonic friendship, but becomes a romance by series end. In addition to the series-spanning story arc, "Monster-of-the-Week" episodes form roughly two-thirds of the episodes. Such stand-alone episodes enrich the show's background while not affecting its ongoing mythology.