Classic analysis of the play defines such trait as ambition. Indeed, although Macbeth is also portrayed as being “brave” and “valiant” he is mostly depicted as being overall ambitious. Indeed, he is initially shown to be a brave and valiant warrior but when confronted to the prophecy of the witches and the nefarious influence of his wife he quickly succumbs to ambition and starts his long series of crimes.
In Act one, not only has Macbeth been confronted with the prophecy of the three witches and its quick partial fulfillment as he is made Thane of Cawdor, he is confronted to the intensity of his own ambition, the strength and nature of his own morality and the manipulative influence of his wife. When King Duncan announces his intention to name Malcolm his heir, the first reaction of Macbeth is to ponder the obstacle that the latter will represent to his ambition of becoming king. His ambition has already caused him to have traitorous thoughts.
Then he is faced with his own morality, knowing that his actions are morally corrupt and sinful and trying to resist the temptation to commit regicide. However, he is unable to resist the mockery of his wife, lady Macbeth and knowingly succumbs to ambition.
In Act two, he is still calculating his possibilities of becoming king, especially when Banquo’s son appears, since he is pondering the fact that because of the prophecy the latter will likely succeed Banquo as king of Scotland. Again, his wife taunts him into carrying out the crime and it is made clear that he has finally succumbed to the temptation of ambition.
After the crime, he regains his composure and becomes once more a man of action, with a clear plan to eliminate everything in his path to become king.