Final answer:
By the end of Act IV, Macbeth has shifted from a noble hero to a power-hungry tyrant, driven by ambition and manipulation from external influences such as the witches and Lady Macbeth.
Step-by-step explanation:
Considering the character descriptions given throughout Macbeth and his actions by the end of Act IV, it becomes clear that Macbeth is power-hungry and ruthless. Macbeth is first described as a valiant hero by the Bloody Soldier and is honored by King Duncan for his loyalty and achievements. However, his encounter with the witches reveals a deep-seated ambition, and under the influence of Lady Macbeth, he betrays his noble qualities by murdering Duncan to ascend to the throne.
By Act IV, the noble traits initially attributed to Macbeth are overshadowed by his treacherous actions. The transformation of Macbeth's character is clear; he has ordered the murders of Banquo and Macduff's family, showcasing his willingness to sacrifice morality for power. This drastic shift indicates that Macbeth has become characterized more by his ruthless and tyrannical behaviors, aligning with option b) Macbeth is power-hungry and ruthless, rather than being simply a victim of circumstance or misunderstood.