A US Marshal was a federal law enforcement official in the United States. One of a Marshal's duties was to escort prisoners. In 2369, while playing the Ancient West holoprogram with his son Alexander, Worf asked the boy what they were supposed to do with Eli Hollander. Alexander replied that they were supposed to wait until the US Marshal came, and then they would take him to Rapid City for his trial. (TNG: "A Fistful of Datas" )