Portia's servant, Balthasar, is the most minor of characters. He appears on stage in only one scene, when Portia sends him with a message to Doctor Bellario in Padua. She asks him to bring "notes and garments" from Bellario to her at a meeting place beside the Venice ferry. Portia begins by emphasizing how much she trusts Balthasar, saying that she has always found him "honest-true," and ends by impressing on him the importance of speed in his mission, telling him that she will be there before he is. Balthasar replies only with a simple affirmative:

Madam, I go with all convenient speed.

This is all we see of Balthasar himself. However, when Portia takes on the role of defending Antonio, the clerk reads a letter to the court from Bellario, introducing Balthasar, "a young doctor of Rome," who, of course, is Portia in disguise.

We do not know whether Portia chooses Balthasar's name because he is a trusted old family retainer, or because he was entrusted with this mission, or whether Bellario simply had no idea what other name to write. What is clear, however, is that Portia, arguably the most major and memorable character in the play, makes a far greater impression on the audience in her disguise as Balthasar than Balthasar ever makes on his own account.