Macbeth is a pretty complicated character throughout the play. At first he is a noble and worthy warrior on the battlefield. He is rewarded by the king--who is not only his superior but also his friend. However, after hearing the prophesies of the witches, he begins to find ways to make those prophesies come true for himself and his wife.
This is the first change we see in Macbeth. He and his wife come up with a plan to murder King Duncan in his own castle the night that they stay over. At first he doesn't want to go through with it. He has reservations and realizes what he's getting into. Then his wife chastises him for not being strong and ambitious enough to go through with the killing. Next he goes through with it and kills Duncan in his sleep. But he forgets to leave the daggers upstairs with the sleeping guards. His wife has to take them back up to make it seem like the guards killed Duncan. At this point he is weak and must have his wife with him to talk him into the deed.
However, after he is crowned king of Scotland, he begins setting up murders on his own. He plots and sets up the deaths of both Banquo and the entire Macduff family. He does this without telling his wife. He has officially grown into a monster. Until he is brought down in the end, he fights to the end. Perhaps he is mad, but he knows well what he is doing.