Macbeth is the tragic hero of the play Macbeth because he fits all of the criteria: he is of noble birth; he is morally good at the start; he has a tragic flaw; his actions affect the entire kingdom; he understands the consequences of his actions; and his actions lead to his death.
Macbeth's father was Thane of Glamis, and Macbeth succeeded his father, making him of noble birth. (Act 1, Scene 3, line 48).
At the beginning of the play, Macbeth is loyal to his country and king and also fights bravely for them. Duncan praises him and his peers look up to him. (Act 1, Scene 2, lines 1-69).
Macbeth's tragic flaw is too much ambition. Once Lady Macbeth convinces him to kill the king, Macbeth becomes power hungry and does whatever he has to to stay atop as king, including killing his best friend (Act 3, Scene 3, lines 1-22), and his enemy's family (Act 4, Scene 2, lines 1-83). .
Macbeth's actions affect the whole kingdom greatly. First, he kills Duncan, Scotland's king (Act 2, Scene 2, lines 1-74). This leaves Scotland with no king until Macbeth is crowned, which is a rather large change. He then kills Banquo, fearing that he and Fleance, his son, would be his down fall (Act 3, Scene 3, lines 1-22).
Near the end of the play, Macbeth recognizes that his actions now have consequences. Since he killed Duncan, he enraged many and is now facing his doom. He realizes that this all stemmed from one murder he committed.
Macduff kills Macbeth as revenge for killing Macduff's family, and also for Malcolm, the rightful king, as Macbeth murdered his father. Once again, because of one murder, chaos ensued. (Act 5, Scene 8, lines 30-105).
For all the above reasons, Macbeth is the tragic hero of Macbeth.