As of Act 1 & 2, various characters have influenced Macbeth: the witches, Lady Macbeth and his own ambition. Although they all played a part in influencing Macbeth, I strongly believe that, with a doubt, Lady Macbeth influenced him the most.

In Act 1, the three witches enlightened Macbeth with 3 prophecies. Two of which have been already fulfilled; however, Macbeth knew only one. The prophecies stated that he would become the thane of Glamis, the thane of Cawdor, and soon to be a king. Later on, the first two of the witches' predictions came true. Which then excited Macbeth, and prompted him in sharing what happened, prior to being crowned the thane of Cawdor, to Lady Macbeth.

Afterwards, in Act 1- scene 5, Lady Macbeth reveals her thoughts of Macbeth in her soliloquy. She feels Macbeth isn't ambitious to begin with but he is also too kind, causing her to be worried he might pass up a chance of taking over the throne. This is revealed when she states: " Yet do I fear thy nature. It is too full of human kindness...Art nor without ambition, but without the illness to attend to it...that I may pour my spirits in thine ear, and chastise with the valour of my tongue all the impedes thee from the golden round which fate metaphysical and doth seem to have thee crowned withal." Having said that, in Act 1 scene 7, Lady Macbeth convinces the doubtful Macbeth into killing Duncan, the King of Scotland (which he does in Act 2 - scene 1).

In conclusion, although it may seem that the witches influenced him in killing the king, it wasn't, because we were told that he wasn't an ambitious man he was actually really kind hearted, thus, he wouldn't have the courage to fulfill the third prophecy. He wasn't prepared to risk being prosecuted for murdering the king of Scotland. Without the influence of his wife, Lady Macbeth, the third prophecy would have never been accomplished.