The first impression we have of Caesar is formed in Act I through the speeches of Cassius. Cassius hates Caesar and resents his rise to such great power in Rome. He describes Caesar in bitter, mocking words, showing his contempt. According to Cassius, Caesar does not deserve the power he wields. Through two specific stories he tells, Cassius presents Caesar as lacking both courage and physical strength. Thus, the first impression of Caesar is that because he is weak, he is not fit to rule Rome.
Brutus listens to Cassius, but offers no such criticism. His concern in regard to Caesar's rule is that he has gained too much power and may prove to be a threat to freedom in Rome. His doubt raises questions immediately in the play in regard to Caesar's nature and intentions. Does he seek all power? Does he wish to become a king in Rome? When Caesar subsequently refuses three times a symbolic crown offered by the people, his actions are viewed skeptically by his critics, leaving this question in regard to his character unresolved.
Caesar's character is further developed by Caesar himself in the second scene of Act II. On the night before the Ides of March, he seems sympathetic as he takes to heart Calpurnia's distress. However, another side is revealed as he throws her feelings aside and decides to go to the Senate once he believes that his not going will raise questions as to his courage. He speaks of himself in the third person, attesting to his own courage. Also, being told that the Senate may offer him a crown seems to firm up his decision, a detail that supports the idea that he seeks to dominate politically and stamp out Roman freedom, Brutus's worst fear. Caesar's behavior in this scene show him to be, most of all, a skillful politician who knows how to preserve power and who seems to seek more.
Finally, Caesar's address to the Senate shortly before his assassination emphasizes his great ego and his inflexibility in ruling Rome. He will not consider the petition presented him to allow the return of a Roman citizen he has banished, and he speaks with cold arrogance in describing himself and his position among fellow Romans:
I could be well moved, if I were as you.
If I could pray to move, prayers would move me;
But I am constant as the Northern Star,
Of whose true-fixed and resting quality
There is no fellow in the firmament.
By this point in the play, Brutus's fears have been confirmed and Caesar has been developed to show that his character has been corrupted by power.
However, even after his death, his character development continues. At Caesar's funeral, Antony presents a radically different view of Caesar. As he addresses the crowd, Antony stresses Caesar's strength and courage in defense of Rome and his love for the Roman people, as evidenced by his generosity toward them in his will.
Throughout the play, then, Caesar's character is developed in numerous, and often conflicting ways, showing him to have been a powerful and complicated figure. The first impression of him as delivered by Cassius proves to be false and misleading. Whatever else might be said of him, Caesar was not a man to dismiss as being weak.