King Duncan of Scotland
Duncan is a mature and effective king who rules Scotland during a time of political upheaval and turmoil. He is too old to command the armies himself and his sons are too young and inexperienced to fight in wars, but he has several great captains under his command, which allows him to remain in power. Those that remain loyal to him do so because they see that his rule is divinely sanctioned. When Macbeth hesitates in his decision to assassinate Duncan, the reason is that he fears Duncan's "virtues / Will plead like angels, trumpet-tongued against the deep damnation of his taking-off" (I.vii.17-18) - that the very heavens will object to the murder of a king so holy. It turns out that Macbeth's fears are justified - on the night of his murder, chimneys are blown down, the earth shakes, owls scream and kill falcons, and horses run wild and eat each other.
The elder son of King Duncan, Malcolm is named the Prince of Cumberland and heir apparent early on in the play. After his father is murdered at Macbeth's castle, he and his younger brother, Donalbain, decide to split up and flee for safety because they will probably be the next targets of the murderers. Although they are safe abroad (Malcolm in England, Donalbain in Ireland), they are not at home to defend themselves against accusations by the Scottish thanes (the equivalent of English earls), that they murdered their own father for the crown. In time, it becomes clear that Macbeth perpetrated the regicide on Duncan, and Macduff seeks out Malcolm in the English court to return to Scotland to claim his birthright and rescue them from Macbeth's tyrannical rule. Malcolm has since been prospering in the English court of Edward the Confessor, a figure remarkably similar to Duncan, and he has learned much about politics and warfare. By the time Macduff comes looking for him, he has already enlisted the aid of Siward, Earl of Northumberland, who...