The subject term, which comes from the latin subjectum, admits of many meanings
If it is synonym of vassal, topic refers to one who is subject to the authority of a superior and is forced to obey him. However, this term was more common once, at the time where there was a different conception of the State. The sovereign was the absolute monarch and the owner of all rights in its territory, while the subjects were "objects" (and not "subjects") rights of the monarch.
Examples: "the error of the leader was to show his weakness to his subjects", "the King always addressed subjects in a friendly manner, in order to secure their confidence and avoid riots", "Lord Scheniltz refuses to continue to be the subject of his Highness".
It can also be of any living being subject to observation, or still what makes the material or the object of a work or discussion.
For Linguistics, the topic is the function in the sentence a term belonging to the category name (or identical), thus giving the verb categories of person and number. This is the subject that practical action.
A subject is also a decorative pattern with figures: "I especially like tapestries to mythological subjects.
Finally, "The subject of the Emperor" is the name of the novel written by the German Heinrich Mann shortly before the first world war, and which was adapted to film by compatriot Wolfgang Staudte.