Don Pedro is the Prince of Aragon. He has just won a war against his illegitimate half-brother Don John. He reconciles himself to his brother, though he doesn’t speak to him much and may merely be keeping him close to keep an eye on him.
Though a bachelor himself, he has a high enough regard for marriage to help Claudio in asking for Hero’s hand and to join in mocking Benedick for his insistence on never marrying. Willing and able to trade barbs with Beatrice at her own level, he soon decides she would be well-matched with Benedick, and entirely hatches the plot to bring them together. Despite all his reasons to distrust his half-brother, he believes Don John’s accusations readily enough to agree to spy on Hero’s window, and swears that if the allegations are true he will join Claudio in disgracing the lady in church to repair his own honor, which is tarnished by having arranged the match. His conviction of his rectitude after the scene in the church is such that he will not offer any hint of apology for his behavior to Leonato, and is able to quickly switch tacks and return to mocking Benedick. Though horrified when it turns out he has been gulled and willing to mourn Hero, he still refuses admit that there was anything wrong with his behavior per se, merely that he acted on faulty information.