The character of Don John is 2-dimensional (as opposed to a 3-dimesnsional or realistic character that displays a variety of emotions, good and bad). Shakespeare relies upon using a stock character in his drama because Don John is simply a plot device. A stock character is a type or 2-dimensional character in drama. Not all of the characters can be fully developed in a play. Stock characters in comedies were common especially in comedies, and Renaissance audiences came to expect them when they went to the theater.
Don John is a character of mischief and trouble. One editor calls him a “malcontent pure and simple.” His plans or schemes to cause trouble for the Prince and his friends create the tension in the plot. Without this stock character, the play would be too simplistic and monotonous.
The reader should also note that during the Renaissance there existed a prejudice against bastards. Many people believed that bastards were unnatural and would commit criminal or evil acts. Although Shakespeare most likely did not share this prejudice, he was well aware of its existence and had no problem with relying on such a prejudice to save unnecessary explanation. Shakespeare did not have to develop Don John or explain his motivation. All he had to do was to say that he was a bastard. For the Renaissance audience, this was explanation enough. Thus Shakespeare could devote more time to developing the characters that were important to him in this play. Another well-known "bastard" from the Shakespeare plays is Edmund in King Lear. Not surprising to the Renaissance audience, Edmund is also an evil character.
Don John is a character of melancholy and gloom, and he wants everybody to be as miserable as himself. In regards to Bakhtin and his carnivalesque theory, Don John is an “anti-comic force.” He is the enemy of fun and joy and happy endings. Such a force causes trouble for most of the comedy, but at the end of the play that force is discovered and rendered powerless.
If there is one word that best describes the character of Don John (and the emotion that motivates him), that word is envy. Don John may envy Claudio as being the favorite of the prince (especially in Act I, Scene 3), but even more likely is that Don John envies Don Pedro. In this regard, Don John may be like Edmund in King Lear. After all, due to a trick of fate or nature, Don John became a bastard. He did not ask to be one. Thus, he may envy his half-brother Don Pedro for being legitimate and thus becoming the legal heir to the property and title of his father. Don John, on the other hand, would inherit nothing, would get nothing.
Francis Bacon wrote an essay entitled “Of Envy” (1601). In it he declared that the kind of people who were most likely to be troubled by envy were “deformed persons, old men, and bastards.” Not many people during the Renaissance would have argued against that point.