Portia is an extraordinarily rich heiress of Belmont constrained by her father’s will to accept in marriage whichever suitor successfully passes the test of the three caskets.
Luckily, as an unsuccessful suitor must swear to never marry, most of them refuse to go as far as the ordeal, but she is still not overly glad of her circumstances. She has no taste for dark-complexioned men, though she is tactful enough not to say so directly to the Prince of Morocco. She is highly hopeful that Bassanio will succeed, but worried enough that she begs him to wait a few days before attempting the task, as she does not want him to leave as he will have to if he fails. By this point she definitely knows which casket is the successful one, and she has a song sung during his meditations that contains many words rhyming with "lead." On being won, she is somewhat uncertain as to what she is, now that all her wealth has passed to Bassanio. She is either wildly generous or has no actual sense of money, offering a massive fortune to Bassanio to help Antonio with Shylock. She is also highly intelligent and trained in law, and knows enough that she quickly conceives a plan to secretly save Antonio’s life disguised as a man. With the help of instructions from her father’s old friend Bellario, she is able to do so, though she drags it out unconscionably, giving Shylock multiple opportunities to stop, but letting him get to the point of killing Antonio before revealing that he cannot and stripping him of his wealth. As thanks for saving Antonio’s life, she receives the ring that she gave Bassanio that he had sworn never to part with. Not best pleased by this, especially as he has earlier sworn he’d give her up to save Antonio, she leads him a merry dance on his return to Belmont, refusing to listen to his protestations of good faith and swearing that she would sleep with the lawyer who had the ring should he come along. Having properly panicked Bassanio, she reveals the trick, to his evident relief. She is also able to let Antonio know that he is not ruined after all, one of his ships having made it to shore, though she refuses to say how she knows.