Betrayal not only drives the plot but also helps characterize certain individuals in the play. The primary character who betrays both King Duncan and Banquo is Macbeth. After receiving favorable prophecies from the three witches and talking to his persuasive wife, Macbeth betrays King Duncan by assassinating him. Before he decided to commit regicide, Macbeth was a loyal supporter of King Duncan and valiantly defended Scotland on the battlefield. Macbeth's treachery emphasizes his dishonest, selfish nature and portrays him as a malevolent, ambitious individual. Macbeth also betrays his close friend and former ally Banquo. In order to cement his legacy, he hires murderers to kill Banquo and his son, Fleance, who narrowly escapes the attack.
Lady Macbeth is another character who betrays King Duncan and is directly responsible for his death. She displays her capacity for dissembling by welcoming King Duncan as a gracious host while simultaneously plotting his murder. She not only masterminds the plot to kill him but also plants the bloody daggers back in his chamber.
Following his father's assassination, Malcolm is suspicious that someone else will betray him, and he flees for England to escape the dangerous environment. One could also say that Macduff betrays his family by fleeing Scotland to join forces with Malcolm. While Macduff is overseas, Macbeth murders his entire family, which fuels Macduff's thirst for revenge. When Macduff arrives back in Scotland, he is more motivated than ever to kill Macbeth—which is exactly what he does in the final battle.
Betrayal drives the plot of the play. First, Macbeth betrays his king, friend, guest, and kinsman when he murders Duncan. Macbeth has always been loyal to the king, and he recently fought valiantly on two different fronts in order to secure Scotland against traitorous rebels and foreign invaders. However, once the Weird Sisters tell him that he'll become Thane of Cawdor and king, and then he actually learns that he's been named the Thane of Cawdor, his ambition consumes him and he eventually betrays his king and country.
Later, Macbeth betrays his former best friend, Banquo, ordering his murder as well as the murder of Banquo's son, Fleance, because the Weird Sisters told Banquo that his descendants would be kings. Macbeth regretted Duncan's murder, but by the time he betrays his best friend, his conscience is basically dead. Betrayal of those by whom one is trusted seems to be a sure way to become utterly morally corrupt.