The X-Files is an science fiction horror drama television series created by Chris Carter. The program originally aired from September 10, 1993 to May 19, 2002 on Fox, 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.