William Shakespeare, the greatest dramatist of his time, personifies evil through the character of Iago in his play ‘Othello’. The play was first performed around 1604-05 and printed in 1622. Whereas Ben Jonson, one of Shakespeare’s contemporaries, portrays a similar character through Mosca in his play ‘Volpone’ which was first performed in the year 1605.
Iago has a mysterious character. He is quiet and yet alluring. “Shakespeare [himself] was obviously fascinated by the man-he gave Iago more lines than any other character in his work-more than Hamlet, King Lear, or Othello.” 
Mosca on the other hand portrays a different kind of evil. He is never quiet but always playing an active part in the game. Iago and Mosca are the devil incarnate. While the malevolence of these two men follows the same path through the majority of their respective plays, their very different personalities are revealed once their treachery is unveiled.
The plots are affected mainly through their actions. They put thoughts into the brains of the rest of the characters, who become puppets in their hands. Some characters in Elizabethan drama are just infinitely bad; they were born that way. Keeping in view this point, we can say that Iago and Mosca need no motive. They just love to see people suffer and adore authority; therefore, they cannot even imagine any other individual commanding them. They both have almost the similar motivations, that is, they want to gain power and the one tactful weapon they have is the use of persuasive speech. They use their excellent rhetoric to exploit the human psychology.
Iago is jealous of the people and their power around him. In the play he expresses openly his jealousy of Cassio and Othello. He is jealous of Cassio's job and of Othello's success as a soldier and with Desdemona. He only professes his desire for revenge and power in the initial speeches. In the opening scene of Othello, Iago explains to Roderigo that Cassio who, "never set a squadron in the field," (I.i.22) was given the rank of Othello's lieutenant while Iago, who mentions his exploits at Rhodes and Cyprus, was given the small position of Othello's ancient. From the very first scene of Iago we learn that he feels cheated, therefore, he might be plotting revenge later on. Roderigo, who tries to console Iago over his fallen state, becomes the first victim of Iago’s malice. Iago, from here, uses this position of ancient to his own convenience. Iago manipulates, he uses his position for personal gain. He says, "I follow him to serve my turn upon him," (I.i.42). By being the ancient, he can gain Othello’s trust and if he is successful in doing so, he can easily feed him with ideas that can become the cause of Othello’s own downfall. Here, Iago says, "I am not what I am," This statement shows that Iago is now going to be behind a veil and plot, never revealing his true identity. This concealment of identity is present in Mosca’s character as well.
Mosca, from the very beginning of the play, has been known as the ‘parasite’. He is feeding on Volpone’s wealth and would not separate himself from it unless he has taken all of it, under his possession. We are aware of Mosca’s intentions from the very beginning. He believes that, “riches are in fortune a greater good than wisdom is in nature.” (I. i) He keeps maneuvering Volpone’s thoughts, flattering him for his great character who very easily falls a victim to Mosca’s false praise. He says,
“You shall have some will swallow
A melting heir as glibly as your Dutch
Will pills of butter, and ne'er purge for it;
Tear forth the fathers of poor families
Out of their beds, and coffin them alive
In some kind clasping prison, where their bones
May be forth-coming, when the flesh is rotten:
But your sweet nature doth abhor these courses;
You lothe the widdow's or the orphan's tears
Should wash your pavements, or their piteous cries
Ring in your roofs,...