The Macbeth we first encounter is an important and valued member of his society and the favorite of his king. His bravery and loyalty are celebrated and, though fierce in battle, we are led to believe that his is a fundamentally good and virtuous nature. By the plays end, however, he has 'supped full of horrors' and is regarded as a 'hell-hound' by his peers. In my opinion, key to this tragic downfall is Macbeth's relationship with his wife, Lady Macbeth, and the influence they exert upon each other.
Within this relationship there is rarely true equality - one partner almost always has undue power or influence over the other. At the beginning of the play, Lady Macbeth seems the controlling influence. But, again, by the time we reach the final act she is deranged and will suffer and die virtually alone. In many ways, charting this private change of influence tells the story of Macbeth.
A renowned warrior and the saviour of his country, Macbeth's authority naturally commands the respect of his countrymen in the opening scenes. There is little sense of this authority or respect in his domestic life. When Lady Macbeth learns that Duncan is to stay at their castle she conceives the opportunity to accelerate Macbeth's progression to the throne. The manner of this progression is the catalyst for all that follows.
Lady Macbeth plays an essential role in Macbeth's murder of Duncan. It remains unlikely that one individual could convince a good and virtuous individual to murder against his or her will. In fact, it is Macbeth who first moots the possibility of usurpation in his letter to Lady Macbeth. And perhaps here we have the first real illuminator of Macbeth's propensity for appalling action. However, in these opening acts much of our ire is reserved for Lady Macbeth. She is a woman of neither serious intelligence nor imagination. She is, nonetheless, possessed of a formidable and domineering strength of character