Final answer:
Lady Macbeth hesitates to kill King Duncan because he resembles her father while sleeping, revealing a rare moment of vulnerability in her ambition-driven character.
Step-by-step explanation:
The character in Macbeth who reflects on their inability to carry out a deed due to the resemblance of the victim to their father is Lady Macbeth. In Act II, Scene II of Shakespeare's play, she says, 'Had he not resembled My father as he slept, I had done't.' This line reveals her hesitation to kill King Duncan herself because he looked like her father while he was sleeping. This moment is significant because it shows a vulnerability in Lady Macbeth's otherwise ruthless character, and exposes an underlying humanity that she suppresses in her pursuit of power.