Calderon

From X-Files Wiki

Dr. Calderon (played by Gerard Plunkett) was a doctor who worked at a pharmaceuticals company and provided special medical service to Emily Sim as part of the Syndicate conspiracy to create an alien/human hybrid. Scully met him while investigating the murder of Marshall Sim's wife. (TXF: "Christmas Carol")

Mulder met Calderon in a much more confrontational manner, pulling a gun on him and demanding that he do more to save Emily's life. Calderon was thoroughly intimidated and hastily fled back to his house, despite being followed by Mulder. There, Calderon met with a pair of alien bounty hunters that killed him and took his appearance to confuse Mulder. In the guise of Calderon, one of the bounty hunters killed John Kresge, but allowed Mulder to escape. (TXF: "Emily")