What is the role of Portia in the Merchant of Venice?
Portia serves several purposes within Shakespeare's The Merchant of Venice.
First, as a wealthy heiress, Portia is the subject of Bassanio's affections... and the attentions of many other suitors. Despite being practically destitute, Bassanio manages to borrow enough money from Shylock, a Jewish lender, (using a friend, Antonio, as the guarantor for the bond) to pass himself off as a "suitable" suitor. Bassanio manages to win Portia's hand in marriage by correctly choosing a lead casket bearing the message, "Who chooseth me must give and hazard all he hath," in a challenge laid out by Portia's late father. Thus, Portia becomes Bassanio's wife.
Second, Portia acts as a lawyer, disguising herself as the male "Balthazar," in order to defend Antonio from the bloodthirsty Shylock, who has come to seize his "pound of flesh" after Antonio has failed to repay the bond owed on behalf of Bassanio. Portia displays stunning intellect and rhetorical agility, and she eventually is able to manipulate Shylock's agreement with Antonio to work against the lender.
Finally, Portia acts as a bearer of good news when in the final act of the play she is able to tell Antonio that his three ships that had allegedly been stranded at sea--which was the reason for his financial crisis and near brush with death in the courts--had actually returned safely to port.