Duke Vincentio is the ruler of Vienna. He does not much enjoy pomp and circumstance, and has spent a great deal of time off in his study, during which time many laws in his city have gone disregarded.
Not wishing to be seen as a tyrant by suddenly changing his mind on the subject, he goes on a trip, leaving his powers in the hands of a man he knows will reestablish the rigors of the laws. At the same time, he decides to find out whether Angelo is in fact as pure as he seems to be, and disguises himself as a monk to keep an eye on matters. He is manipulative, though always with reasonably good motives. He prepares Claudio to die even though fully intending to save his life. He has known for a long time about Mariana’s betrayal by Angelo, and decides to take this opportunity to fix the situation for her. He also takes the opportunity of his disguise to try and find out what people think of him, and is shocked at Lucio’s slanders, as he thinks rather well of himself. Having a flair for the theatrical, he arranges matters to have the most dramatic reveal possible. Once he has let everyone know that he has been there all along and could have stepped in at any moment to stop things from going too far, that he could have demoted Angelo earlier and easily have saved Claudio’s life, but preferred to remain disguised, watch how things went and make them more interesting, he asks Isabella to marry him. She gives no answer, and he has to ask twice. He is very concerned that his own reputation be upheld, and is a firm defender of monarchs’ rights to be considered the best of men.