Was King Duncan a king?

Duncan is the king of Scotland when the play opens and it is in his service that Macbeth and Banquo have fought to defeat his enemies. Duncan is highly appreciative of the services rendered to him by these generals. He rewards Macbeth for his (Macbeth’s) achievement in the battle conferring the title of the Thane of Cawdor upon him. In the play Macbeth Duncan has been portrayed as a kind, mild, benevolent and popular monarch. 

Most of his actions in the play are marked by a rare generosity. His instantaneous decision to visit Macbeth’s castle as a show of honour is the outcome of a generous heart. His final act of generosity, his sending forth great largess to Macbeth’s offices and greeting Lady Macbeth with a diamond, stand in sharp contrast to the cruel machinations of host and hostess. In addition to being gracious and generous, Duncan also impresses us as an embodiment of virtue.  

Macbeth himself recognizes it. Before murdering Duncan, Macbeth fears that the murder of such a noble king will arouse a flood of pity in the hearts of people and provoke storm of protest from them. Duncan is a representative of the principle of goodness in the play Macbeth. Macbeth’s murdering such a king is an outrage, a violation of the natural order of things. Murder is a hateful crime under all  circumstances but the murder of such as a good man becomes doubly hateful.