sentences:  If Blake and his crew represent Robin Hood and his Merry Men, then the Federation forces, personified by the obsessive, psychopathic Space Commander Travis and his superior, the beautiful but ruthless Supreme Commander Servalan, represent Guy of Gisbourne and the Sheriff of Nottingham.A common theme of Nation's science fiction is the depiction of post-apocalyptic societies, as in several of his "Doctor Who" serials, for example "The Daleks", "Death to the Daleks" and "The Android Invasion" and in his series "Survivors", which Nation created before "Blake's 7".Post-apocalyptic societies feature in several "Blake's 7" episodes including "Duel", "Deliverance", "City at the Edge of the World" and "Terminal".