Macbeth, whilst the Witches and Lady Macbeth influence him, is ultimately responsible for his downfall. In William Shakespeare's play, Macbeth is a tragic hero, who is destroyed by his own desperate lust for power. At the beginning of the play he is portrayed as a loyal soldier, lauded as a "valiant cousin" by his peers. When given the role as Thane of Cawdor, his "black and deep desires" shine through, as the witches' prophesy begins to come true, prompting him to take the icy path toward the life of a tyrannical leader.
Macbeth is firstly influenced by the witches, who install the prophecy into his mind saying "all hail king that shalt be hereafter!" He blindly believes the prophesy without any proof initially. He refuses to dismiss the words of the witches like Banquo and misinterprets them as an assassination contract; they provide the basis for his motivations, but they do not explicitly tell him to murder the king, he does that on his own. The witches are motivated by their lust for mischief, saying, "Double double, toil and trouble." They specifically target Macbeth as he lacks capability to think for himself and can be influenced to the point of his own destruction. He makes a perfect target because of his main purpose in life, murder - it's his profession and his easy to please personality that makes him the ultimate toy for the witches, which is undoubtedly proven in his actions later in the play. Without the intervention of the witches, Macbeth's ambition would never have been thrust toward the idea of being king and he would've never considered murdering the man he called king; however he still manages to question his motivations and is only pushed over the edge by his equally power hungry wife.
Lady Macbeth acts as the facilitator of Macbeth's "vaulting ambition," she enables him to overcome his objections to murder for several reasons, by using grotesque imagery describing the contractual nature of making a promise and by convincing Macbeth that he will get away with their scheme.
