The pilot introduced the two main characters, Fox Mulder and Dana Scully who were portrayed by David Duchovny and Gillian Anderson respectively. The episode also featured William B. Davis, Charles Cioffi and Zachary Ansley as the recurring characters of the Smoking Man, Scott Blevins and Billy Miles. The Smoking Man would go on to become the series' signature antagonist, appearing in every season except the eighth. The episode follows FBI Special Agents Mulder and Scully on their first X-File case together, investigating a string of deaths which Mulder believes to be alien experiments.