How is Macbeth presented?

The character Macbeth is first presented as a good man who has won renown in battle and is loyal to his king. However, after he meets the three witches, who seemingly present a prophecy that Macbeth will become king of Scotland, this begins to change. 
As Macbeth considers the possibility that he should take action in becoming king, namely by killing King Duncan, his good nature is thrown into conflict with his newfound ambition. With the encouragement of his wife, Lady Macbeth, Macbeth gives in to his ambition and kills the king. The good man in Macbeth is horrified by what he has done, even as he ascends to the throne.  
The tension between who he was and who he is to become plays out over the rest of the play. After having his friend Banquo killed in order to solidify the crown for his possible heirs, Macbeth begins to be haunted by visions of his dead friend. At this point, Macbeth the king becomes more authoritarian, as well as more detached from his subjects, including his wife. 
By the last act of the play, the good man that Macbeth was before has been fully consumed by Macbeth the tyrant. His primary focus is to preserve his reign at any cost. Even learning of the death of Lady Macbeth does nothing to dissuade him from his objective. In the end, Macbeth becomes ruthless and cruel, a man driven mad by ambition and the horror of what he did to fulfill that ambition. It is only his death that releases Macbeth from the fallen man he became.