Andy Evans is the main antagonist of Speak.
Andy Evans was a senior in high school as well as the rapist of Melinda Sordino. He met Melinda at a party, and he took her into the woods to rape her. Melinda tried to call 911 to help her, but she didn't know what to tell them. This led to several people getting arrested at the party, and Melinda becoming an outcast.
Later on in the story, Andy began to date Melinda's ex-friend, Rachel. When she discovered the truth about what he had done to Melinda, he angrily went to her, and he tried to rape her a second time. This caused Melinda to finally stand up for herself, and he was found out.
Andy was described as sleazy and narcissistic, and he was also noted as being very handsome looking. Despite this, he was actually a repulsive individual underneath. He had a disturbing history of sexually assaulting girls, and it's heavily implied that Melinda wasn't the only girl that he raped.
Andy was also a sadist as shown when he was asking Melinda if she remembered their time together and taking great enjoyment from it.