My first time actually posting here. Please be gentle. :)
For failed book heroes, I immediately thought of Carillon from Jennifer Roberson's Cheysuli Chronicles, specifically book two, The Song of Homana.
It has been a few years since I've read it, and I've forgotten a great deal (intentionally), so my comment on it will be brief, and spoilery.
In book two, Carillon is a young king. He meets the villain's daughter, and decides to marry her. She has other ideas, but he doesn't care. He threatens to send men to take her by force if she won't marry him willingly. So, she winds up marrying him, and bearing a child. And tries to kill him near the end. So, at the end of the book, the woman he'd forced into marriage and raped, gets locked in a tower, where she's to spend the rest of her life, never to see her child again. Just need to repeat: The "hero" rapes the "villain" and then takes away her child.
Doesn't sound like a hero to me. She doesn't sound like a villain to me, just a victim. I have refused to read anything by Jennifer Roberson ever since. People have told me her other work is better, but I find that one so inexcusable that I have no intention of giving her another chance.