Leroy is Minny's husband. He physically abuses her on a regular basis, and tries to kill her at the end of the novel when he finds out he lost his job because of his wife. Leroy is partially based on Clyde, the husband of Stockett's childhood maid, Demetrie. In an interview with The Telegraph, Stockett talks a little bit about Demetrie's conflicted relationship with her husband. (Read about it here.)
Leroy isn't a fully fleshed-out character – we only see him in a few scenes, but he's important to the novel. Namely, he brings out the contradictions in Minny's character – she seems so strong, so tough, so unbreakable when we first meet her. But when it comes to Leroy, she's totally vulnerable and at his mercy. Why? Because she loves him, or thinks she loves him. Leaving him, and realizing love doesn't have to hurt, is a super important part of Minny's story.