Dark Man was a government agent.
He chased Max Fenig to retrieve a device he was carrying stolen from a government contractor. He got on flight 549 along with Fenig in order to take the package from him in flight. After he had assembled his gun in the plane bathroom, however, the plane shook as it was intercepted by a UFO. He saw Fenig abducted, helpless to watch as he could not fire his gun. He was sucked down the aisle of the plane when the craft put Fenig back in the plane. (TXF: "Tempus Fugit", "Max")