Final answer:
After Duncan's murder in Act II of 'Macbeth', Macbeth becomes more resolved and ruthless, no longer needing encouragement to commit further acts of violence. This marks his transformation into a character capable of cold-blooded murder on his own volition.
Step-by-step explanation:
Macbeth's Transformation After Duncan's Murder
After the murder of Duncan in Act II of Macbeth, the character of Macbeth undergoes a significant transformation. His character evolves from one that is hesitant and in need of encouragement to commit the deed, to one that is more resolved and ruthless. Initially, Macbeth is conflicted about killing Duncan, and it is Lady Macbeth who chastises his hesitancy and questions his manhood. However, following the murder, Macbeth begins to exhibit a cold-blooded nature, indicating that he no longer requires external prompting to commit violent acts. This is evidenced in his statement, "I am settled, and bend up each corporal agent to this terrible feat." Additionally, while he displays a semblance of guilt in the aftermath, such as hearing voices saying "Macbeth does murder sleep", this guilt does not deter him from further violent actions. Instead, it compounds his troubles, leading to increased paranoia and aggression as the play progresses.
Therefore, the most accurate description of Macbeth's change after Duncan's murder would be that he no longer needs encouragement to kill someone in cold blood. Although he does not become openly proud of his actions, nor does he stop lying about them, the ease with which he subsequently plots Banquo's murder and the massacre at Macduff's castle demonstrates his transformation into a more autonomously violent character.