What does it mean to be a man?

To me a man is standing up for not only what you believe in but also doing whats right for your family. I do not agree with Lady Macbeth if she were a woman then she would not be forcing her husband to murder the king. In fact if Macbeth were a man then he would have stood up to his wife and said how he truly felt. I feel that a man should always be minded of his own personal feelings.

who's really driving the ambitions of killing the king?

The true "brains behind the operation" would have to be Lady Macbeth. I only say this because Macbeth does want to become king but he has no kind of backbone. So in turn she actually decides to convince her husband to kill the king. If she comes in and takes controll then it would be her running the country not her husband. Like Hilliary and Bill as they say. Hilliary Clinton ran the country not Bill. The same would be with Lady Macbeth and Macbeth.