Duncan is the good, trusting king whose murder is the play's central crime, and his virtues are Macbeth's own best argument against killing him. Macbeth admits Duncan "Hath borne his faculties so meek" that his virtues "Will plead like angels, trumpet-tongued" (Act 1, Scene 7).

He matters in Act 1, Scenes 2, 4 and 6, is killed offstage during Act 2, Scene 2 while Lady Macbeth waits on stage ("He is about it"), and is remembered in Act 4, Scene 3 as "a most sainted king".

"There's no art / To find the mind's construction in the face" (Act 1, Scene 4). He says it of the traitor Cawdor seconds before Macbeth walks in. Dramatic irony: he is about to trust another face.
"I have begun to plant thee, and will labour / To make thee full of growing." (Act 1, Scene 4). The king as a gardener, nurturing loyalty. Macbeth cuts down the man who planted him.

Holinshed's Duncan is "so soft and gentle of nature" that Makbeth attacks his "softnes" in punishing offenders; Shakespeare drops the criticism, which makes the murder more monstrous. Use Duncan as the benchmark of good kingship, and ask whether his trust is a flaw in a world of false faces.

He matters in Act 1, Scenes 2, 4 and 6, is killed offstage during Act 2, Scene 2 while Lady Macbeth waits on stage ("He is about it"), and is remembered in Act 4, Scene 3 as "a most sainted king".

"There's no art / To find the mind's construction in the face" (Act 1, Scene 4). He says it of the traitor Cawdor seconds before Macbeth walks in. Dramatic irony: he is about to trust another face.
"I have begun to plant thee, and will labour / To make thee full of growing." (Act 1, Scene 4). The king as a gardener, nurturing loyalty. Macbeth cuts down the man who planted him.