Who is ultimately responsible for Macbeth's downfall?

In Macbeth by William Shakespeare, the three witches provide Macbeth with a prophesy, saying that he will be Thane of Cawdor and eventually King of Scotland. At this point, a seed is planted in Macbeth's mind. He is strangely receptive of the idea, but he also is afraid to even think upon such a prophecy. It is clear that Macbeth is nervous about even thinking of becoming King of Scotland for he realizes that King...

In Macbeth by William Shakespeare, the three witches provide Macbeth with a prophesy, saying that he will be Thane of Cawdor and eventually King of Scotland. At this point, a seed is planted in Macbeth's mind. He is strangely receptive of the idea, but he also is afraid to even think upon such a prophecy. It is clear that Macbeth is nervous about even thinking of becoming King of Scotland for he realizes that King Duncan will have to be killed first.

When Duncan pays a visit to Macbeth, Lady Macbeth sees an opportunity to kill King Duncan. In fact, during the banquet, Lady Macbeth seeks out her husband when he leaves the dining hall at the banquet. She questions Macbeth about his disappearance. Macbeth informs her that he has changed his mind. He no longer wants to kill King Duncan. He matter-of-factly states that he and his wife will not proceed in this murderous intent:

We will proceed no further in this business. He has recently honored me and I now have the Golden opinions from all sorts of people.

Lady Macbeth will not take no for an answer. She is ultimately responsible for King Duncan's death which in turn leads to Macbeth's downfall. Clearly, Macbeth has changed his mind in killing Duncan, but Lady Macbeth insults her husband's manhood.

Would you have the crown
Which you believe to be the ornament of life,
And yet live like a coward...?

As a brave soldier, Macbeth is affected by her scorn in calling him a coward. She knows exactly what to say to talk Macbeth into completing the murder of Duncan. In some ways, Lady Macbeth is more power hungry that Macbeth. She insults his manhood, knowing that he will decide to kill Duncan. If she had not used her power of persuasion, Macbeth would not have killed Duncan. Macbeth had changed his mind. Macbeth seemed to be content in the honors Duncan has bestowed upon him and has clearly changed his mind about murdering Duncan.

Lady Macbeth persuaded her husband to kill King Duncan. Ultimately, she would not rest until Macbeth had become King of Scotland. Ultimately, she is responsible for Macbeth's downfall.