Greg Walker is an American television producer and writer best known for his work on the procedural drama "Without a Trace. " Walker got his start in TV working as a story editor on Chris Carter's hit paranormal series "The X-Files" and the creator's quickly cancelled "Harsh Realm," and he also wrote episodes of both shows. In 2001, Walker began contributing to the Superman TV drama "Smallville" primarily as a co-producer, though he also wrote a few episodes of the popular series. The following year, Walker signed on to the investigative drama "Without a Trace," starring Anthony LaPaglia, which focused on missing persons cases. During the course of the New York City-set show's seven seasons, Walker served extensively as a producer, penned more than 20 scripts, and also directed two episodes. After the '09 finale of "Without a Trace," Walker worked as a producer and writer on the short-lived medical drama "Three Rivers."