In "Juilius Caesar," Caesar himself describes Cassius as "lean and hungry," a man who thinks too much and is "dangerous" (I, ii, 193-195).
Cassius is these things and more. He is envious of Caesar, speaking of him as a Colossus. Cassius is manipulative of Brutus, telling him
I have not from your eyes that gentleness/And show of love as I was wont to have (I,ii,32-33)
In his manipulations, he is fauning before Brutus, flattering him in order to further sway him to think as he does. Cassius, then, is suggestive, telling Brutus that they groan "underneath this age's yoke" (I,ii,61). He is seductive in his language to Brutus, telling him
I, your glass/Will modestly discover to yourself/That of yourself which you yet know not of. (I,ii,68-70)
Certainly, Cassius is deceptive and dishonorable because he deceives Brutus by playing to Brutus's own sense of honor:
I know that virtue to be in you, Brutus,/As well as I do know your outward favor./Well, honor is the subject of my story...(I,ii,90-93)
In truth, honor is not the subject of his story. He leads Brutus to believe that he has the same noble principles as Brutus when it is power that Cassius desires, not the good of Rome, as Brutus wants.
Clearly, Cassius is shrewd as he knows how to sway his brother-in-law, Brutus. Later in the play, Cassius is quarrelsome with Brutus, but does he defer to Brutus, who is well-respected, thus again showing shredness.
Cassius is exceedingly clever. Caesar says he can see right through men. He is also very dangerous, according to Caesar, who judges him correctly as it turns out.
Cassius is miserly. He loves money and hates to part with it.
He is articulate, persuasive, manipulative. He manages to persuade Brutus to take part in the plot to assassinate Caesar, which is probably something no one else could have done.
Cassius is courageous. He is exceedingly proud. He is emotional, in contrast to his friend and partner Brutus, who is philosophical.
Selfish - Throughout the play he makes it clear that he is looking out for himself first and foremost.
Extroverted - in contrast to Brutus, who is introverted.
Hot-tempered - also in contrast to Brutus.