Final answer:
Duncan is the father of Malcolm and Donalbain.
Step-by-step explanation:
Duncan is the father of Malcolm and Donalbain.
In William Shakespeare's play "Macbeth," Duncan is the king of Scotland and the father of Malcolm and Donalbain. Therefore, Duncan is their father. This relationship is a crucial element in the play, as the events that unfold, including Macbeth's rise to power, are intricately tied to the Scottish royal family and the consequences of Duncan's murder.