In Shakespeare's Macbeth, Macbeth changes once he kills Duncan and recovers from the act.
Before and immediately after he kills Duncan, he plays the role usually associated with females, showing concern for Duncan, since Duncan has been a fair and just king, has treated Macbeth well, and is staying under Macbeth's roof, so to speak, and is expecting Macbeth's protection as his host. Macbeth even worries about betraying the trust others have put in him before he kills the king: he worries about what others think of him.
Once he kills Duncan and emotionally and mentally recovers from the killing, however, Macbeth worries no more about what others think of him, about anything as trivial as hospitality, or about fairness or justice. After killing Duncan he shows no more characteristics normally associated with females.
Macbeth orders the killings of Banquo and Fleance, and, when he can't get at Macduff, orders the slaughter of his family. Any "scruples" Macbeth had have vanished. He becomes the aggressive, murdering male his wife earlier wishes him to be, and in fact wishes herself to be.
Ironically, as the play progresses and Macbeth relishes (sort of, at least) his dominant, male role and Lady Macbeth becomes riddled with guilt (they reverse roles, therefore), Macbeth stops collaborating with her and figuratively shuts her out of his plans (such as killing Banquo, etc.).
In Macbeth, Lady Macbeth undergoes the following changes:
- Act I: she casts off her feminine limitations ("unsex me here") and convinces Macbeth to be a man and kill Duncan.
- Act II: she shows weakness by not being able to murder Duncan; she's a good actress who pretends to faint when hearing the news of Duncan's murder.
- Act III: she continues to castigate Macbeth publicly for being weak when he sees the ghost. Ironically, her mental breakdown will shortly follow. Macbeth refuses to consult her in the murders of Banquo and Fleance.
- Act IV: Lady Macbeth is offstage here.
- Act V: Lady Macbeth's madness is shocking. She sleepwalks and sleeptalks and continually washes her hands of blood that isn't there. She confesses to helping kill Duncan unwittingly. Later, she will commit suicide offstage.
So, Lady Macbeth goes from being a vacuous vessel in Act I to being filled with guilt and madness by Act V.