Macbeth: He is the protagonist of the play and is initially depicted as a valiant, heroic Scottish general. After defeating Macdonwald, the Norwegian army, and the Thane of Cawdor, Macbeth receives a favorable prophecy from the Three Witches, who name him Thane of Cawdor and future king. Macbeth becomes consumed by his ambition and begins to contemplate killing King Duncan and usurping power. He informs his equally ambitious wife about the witches' prophecies and promises to follow through with her murderous plan to commit regicide.

Banquo: He is a brave, noble general who fights valiantly alongside Macbeth at the beginning of the play. He also receives a favorable prophecy from the Three Witches but is much more discerning and less ambitious than Macbeth.

King Duncan: In act one, Duncan is portrayed as a benevolent, compassionate ruler who rewards Macbeth for his courageous leadership on the battlefield by naming him the Thane of Cawdor. He is unaware of Macbeth's prophecy and ambitious plan to usurp power.

Lady Macbeth: Macbeth's ambitious wife is introduced in act one and reads her husband's letter regarding the favorable prophecy from the Three Witches. She is portrayed as a driven woman who vows to persuade her husband into assassinating King Duncan to attain the Scottish throne. In scene seven, Lady Macbeth challenges her husband's masculinity and convinces him to follow through with her murderous plan.

Malcolm: His character is significant because he is King Duncan's son and next in line to become king. In scene four, Duncan names Malcolm to succeed him as king, and Macbeth views him as another obstacle to overcome. Once Macbeth discovers that Malcolm will inherit his father's throne, he once again expresses his ambitious nature by thinking about how to murder Malcolm.

Act I includes these key characters:

1. King Duncan: His murder drives the play; his goodness makes Macbeth's regicide even more abominable.
2. Macbeth: He is the central figure, the protagonist, in the play.
3. Banquo: As a foil to Macbeth, Banquo is especially important; his murder later in the play shows Macbeth's further descent into evil.
4. Lady Macbeth: As Macbeth's wife, her character is very important; she plans Duncan's murder and exerts tremendous influence upon Macbeth to follow through. Without Lady Macbreth, Macbeth might not have actually killed the king.
5. Malcolm: As King Duncan's son, Malcolm is the rightful heir to the Scottish throne; after killing Duncan, Macbeth casts guilt on Malcolm and his brother, forcing them to leave Scotland; Malcolm will not give up until Macbeth is defeated.