Deputy to the duke. Angelo is subject to two main interpretations. He can be viewed as a thoroughly evil man, hypocritical in his pose of morality, whose lust for Isabella is true to character; or he can be seen as a basically moral man who succumbs to temptation upon one occasion.
In support of the first view, critics point out his treacherous and heartless desertion of Mariana, prior to the action of this play, showing a history of immorality. The duke, suspecting the corruption beneath Angelo's facade of righteousness, leaves him in charge to test his true character. Angelo proceeds to convict Claudio of a most human crime. He is deaf to Isabella's pleas for mercy but promises to save her brother if she will have sexual intercourse with him. Believing that Isabella has shared his bed, Angelo compounds his crime and cruelty by ordering Claudio's execution.
It can be argued, however, that the duke leaves Angelo in charge because of a genuine regard for his judgement and virtue. Angelo tries to resist the temptation Isabella presents, seeking aid through prayer (in which his detractors see no sincerity). His final repentance is seen by some as evidence of his basic goodness and by others as an insincere token apology.
Perhaps a true reading of Angelo's character lies somewhere in between. Sincere in his adherence to the letter of the law, he neglects mercy. His tightly contained lower instincts burst forth with a vengeance when too strong a temptation is thrown in his path. Horrified at his own crime, he orders Claudio's execution to save himself, confident that Claudio is, after all, guilty. When the truth is discovered, he is relieved to end the deception and begs that justice without mercy be his punishment.
It is well to remember here that Shakespeare's Angelo is milder than the deputies of the sources. If Shakespeare intended to present a completely evil man, why did he not have Angelo send Claudio's head to Isabella as his counterparts did?