From the onset of Macbeth, things are not what they seem, as "fair is foul" and the witches will come to influence or at least affect Macbeth's actions, with disastrous consequences.
The very decent and respected Macbeth, favored by his king- "brave Macbeth"(I.ii.16) - and awarded for his valor allows his "vaulting ambition" to get in the way of any natural progression or ascendancy. We already see the beginnings of the change in Macbeth when, faced with the same images as Banquo, and both with promises of great things - if not for themselves, their heirs - Macbeth and Banquo's responses are so very different.
Whilst Macbeth and Banquo are still considering the great news, they are greeted with the reality of it. Macbeth is confused - "cannot be ill; cannot be good" - but his paranoia is beginning to develop as he is seeing the work of the witches, rather than the natural progression after battle. He is already wondering how he will overcome the problem of the Prince of Cumberland(Duncan's son Malcolm)- "for in my way it lies."(I.iv.50). A strong leader would now develop his skills in the position afforded him whereas a dictator - or the makings of one - would immediately start working on his next scheme.
A good leader always has a strong support system and Lady Macbeth would do anything, to the point of "unsex(ing)" herself, to support her husband. She is harsh and seemingly mean in her condescending manner; Macbeth only a man when he "durst do it."(I.vii.49) So convincing is Lady Macbeth and the image of her having "dash'd the brains out" of an infant is so compelling that this can only serve to promote Macbeth's over-zealousness. A despot needs someone equally as driven as himself which person, Macbeth has certainly found in his "dearest partner of greatness." (I.v.9)
The descent into the loathsome world that becomes Macbeth's reality is fast. He falters only momentarily and will "proceed no further" (I.vii.32) but having been convinced, he is "settled" and ready to attempt this "terrible feat" his only concern being that he should not be caught - "False face must hide what the false heart doth know." (82) At this point, Macbeth is fully aware of what he is about to do. His subsequent disorientation when the daggers appear "from the heat-oppressed brain" (II.i.39) is indicative of things to come, a foreboding that his paranoia will intensify.
A strong leader develops as he learns how to adapt and use his power to suit his environment and the needs of those who rely on him. A dictator realizes that he has power that he can use and abuse to suit his OWN ends. Manipulating situations is a ploy used by many autocratic leaders. Having obtained a position of power, Macbeth will not stop until it is absolute, feeling safe in the knowledge that "none of woman born" can stand in his way. (IV.i.80)
Lady Macbeth his driving force is now less instrumental in his plans. Typical of a dictator, Macbeth begins to trust external forces - the witches - and his confidence spurs him on. Lady Macbeth will "applaud the deed"(III.ii.46). There is no stopping Macbeth as all reason escapes him. Madness is reinforced by his refusal to back down, even at the certainty of death. Even when he hears of Lady Macbeth's death and his life is nothing more than "a tale ....signifying nothing"(V.v.26), it does not occur to him to surrender. Macbeth realizes that the witches are nothing more than "juggling fiends" (V.viii.19) and is killed.
Surely one of the best examples that demonstrates how Macbeth is a dictator and not just a strong leader comes in Act IV scene 1 when Lennox tells him about Macduff's flight to England to join the opponents of Macbeth's rule. Macbeth has just heard the extended prophecy of the witches in this scene, and in his soliloquy he recognises how accurate they were:
And even now,
To crown my thoughts with acts, be it thought and done:
The castle of Macduff I will surprise;
Seize upon Fife; give to th'edge o'th'sword
His wife, his babes, and all unfortunate souls
That trace him in his line.
Arguably the way that Macbeth feels so threatened by Macduff's desertion of Scotland and the grim and unyielding way that he determines to punish all of his family is the act of a dictator who is unable to brook any opposition to his power and is actually very insecure in the position that he holds. A strong leader would have recognised that it would be more counterproductive to kill Macduff's family in this way and would have not engaged in such brute acts of savagery. Macbeth, by so doing, unwittingly sows the seeds of his own destruction.