Mulder's ultimate goal was to uncover what he believed to be a government conspiracy to hide the truth about alien life, and to find out what had happened to his sister. His quest and belief in the existence of aliens was, for most of the series, the driving force of the plot, or mytharc. However, during a period of time after Scully's cancer went into remission (season 5), Mulder was convinced by Michael Kritschgau that aliens did not in fact exist, and that the government conspirators had merely concocted that threat as a smokescreen, to justify military activities and toy with him.