* Don John: The villain of the play, Don John orchestrates the entire plot to ruin Hero's reputation and prevent her marriage. He is the one who spreads the false rumor about Hero's infidelity, and he does so with the specific intention of hurting Claudio and causing chaos. He actively speaks against Hero, but his words are malicious and intended to deceive.
* Claudio: While not technically "speaking against" Hero in the sense of directly accusing her, Claudio believes the lies spread by Don John and breaks off the wedding in a public and humiliating manner. He is manipulated by Don John, but he also chooses to believe the accusations without investigating further. His actions are motivated by his own insecurity and pride, leading him to act against Hero based on false information.
It's important to note that neither of these characters actually *knows* the truth about Hero. Their actions are driven by deceit and misjudgment, ultimately leading to a great deal of pain and turmoil for Hero and her family.