And then you feature him in a prequel.
Aesthetically, you have two choices.
1. He's a thorough-going scoundrel the length of the story.
2. He's a good character at the beginning and goes rotten by the end.
Which gives you a problem for which there is a technical term: Not Fun At All. (And the first also lacks character development.) I will not like that story without it having some compensating excellencies. (In fact, I will never like such a story without some compensating excellencies, but if it's not a prequel, you're not boxed in.)
On the other hand, it seems a lot of writers agree with me about the Not Fun At All aspect. Unfortunately instead of not writing a prequel, they proceed to clean him up before the work in which he reformed. Which often enough, means that they gut that work. A reformation from a much nicer character than you knew is not as much fun as a scoundrel's reformation.