ASAC (Assistant Special Agent in Charge) is a position within the Federal Bureau of Investigation. (TXF: "Squeeze", et al.) The position may be held by an Assistant Director on a particular case. (TXF: "Provenance") In the FBI hierarchy, ASACs are higher than agents, whom they are responsible for. (TXF: "Squeeze", et al.) In 1989, Reggie Purdue was Agent Fox Mulder's ASAC. (TXF: "Young at Heart", "Unusual Suspects")