MacBeth

The Three Witches
The plan to kill Duncan
Killing Duncan
the three witches tell Macbeth that he will become the Thane of Cawdor and then become King. Banquo is told that his sons will become kings
Once Macbeth comes home he informs lady Macbeth about the witches and the prophecies he got told. Lady Macbeth told him to not be a coward and kill him so he could take the throne for himself
Since King Duncan was visiting Macbeth and staying the night this was the perfect chance to kill him. So he waited until Duncan fell asleep and killed him.