Lieutenant Commander Calvin "Cal" Hudson was Starfleet's first attaché to the Federation colonies in the Demilitarized Zone. Hudson and Benjamin Sisko were close personal friends, having graduated from Starfleet Academy together. Hudson also knew Curzon Dax, who was apparently privy to personal information concerning the officer. He was married to Gretchen Hudson, who died in the late 2360s.
Hudson was leading a double life. Although assigned by Starfleet as the attaché to the planets in the Demilitarized Zone, he was an influential leader of the Maquis. After years of seeing the suffering and abuse of the colonists by the Cardassians, he joined the Maquis. He used his Starfleet position to secure intelligence and supplies for the Maquis. In 2370, Sisko uncovered Hudson's deception during the investigation of the explosion of the Bok'Nor and the kidnapping of Gul Dukat. (DS9: "The Maquis, Part I", "The Maquis, Part II")