The changes in Cassius are interesting and sometimes perplexing. As the drama gets underway, it is Cassius who strategizes, motivates, and manipulates a band of powerful Roman senators in the daring and dangerous public assassination of Julius Caesar. Once Brutus joins the conspiracy, however, as well as after Caesar's death, Cassius seems to assign himself to living in Brutus's shadow. Time after time as the play continues, Cassius ignores his better judgment and defers to Brutus's decisions, with catastrophic results. The man who was not afraid to assassinate the most powerful figure in Rome surprisingly will not confront Brutus over matters of military strategy that will determine their victory or defeat.
At the beginning of the play, Cassius desires Caesar's destruction primarily for personal reasons. He is jealous of Caesar's great power and bitterly resentful that he, Cassius, has been surpassed by one whom he sees as being unworthy of such power. Cassius sees himself as being far superior to Caesar.
At no time, however, before Caesar's assassination does Cassius indicate that he seeks to profit from the ruler's death. After Caesar's death, Cassius does seek personal profits. He takes bribes from those whose lands he and Brutus pass through with their army during the war with Antony and Octavius. It is never made clear what Cassius gives in exchange for the money he accepts in bribes, but Brutus is infuriated that Cassius would engage in this behavior. He castigates Cassius for selling his "offices," meaning that Cassius was profiting from the power taken from Caesar by killing him. Brutus is also disgusted that Cassius has taken money from people who are very poor.
At the conclusion of the play, Cassius bears little resemblance to the man he had been while he plotted and organized the conspiracy to murder Caesar, except for this. He remains selfish and corrupt.
A most complex and ironic character, Cassius of Shakespeare's Julius Caesar, moves from being one who follow Epicurus by believing that the gods have no interest in men's lives--
The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings (2.1.140-141)--
to a man who fears omens as in Act V, scene i when Cassius tells his friends,
You know that I held Epicurus strong,
And his opinion; now I change my mind.
And partly credit things that do preage.
Coming from Sardis, on our former ensign
Two mighty eagles fell, and there they perched,
Gorging and feeding from our soldiers' hands,
Who to Philippi here consorted us.
This morning are they fled away and gone,
And in their steads do ravens, crows, and kites
Fly o'er our heads and downward look on us....(5.1.83-92)
In the beginning of the play, Cassius is also a man of tremendous confidence, who has fought against Caesar at Pompey and is later pardoned. In fact, he considers himself much like the hero Aeneas as he boasts of having saved Caesar from drowning in the Tiber River. He orchestrates the conspiracy as he portrays Caesar as a dangerous and unhealthy tyrant and forges letters to sway Brutus to join the conspirators; yet, against his wiser judgment, he acquiesces to Brutus's wishes to allow Antony to speak before the Romans, and in emotional arguments with Brutus in Act IV, he concedes to Brutus to advance on the Philippi when he knows that they should make the enemy come to them, again acting against his better judgment. In the final act, Cassius becomes a truly tragic figure as he must ask his bondman Pindarus to watch Titinius because "his sight was ever thick"--a loss of sight, critics note, that is symbolic of his loss understanding.
Thus, two of greatest changes that occur in Cassius are his move from being an Epicurean to one who believes in superstitions and fear omens, and from being a villain capable of wise decisions, to a tragic figure who defers repeatedly to Brutus's wishes, wishes that cause their defeat and deaths.
Thank-you very much for your answers. They are VERY helpful!