4. Denny Woods
What was this guys' deal?! Denny Woods (Mykelti Williamson) used to be partners with Voight, but an instance in which Voight caught up arresting the wrong suspect led to him being suspended. Woods was able to rebuild his career as an internal auditor, and he made it his mission to give Voight a hard time.
The thing that's so frustrating about Woods, other than the villainous (and excellent) performance turned in by Williamson, is the fact that he was caught fair and square. Voight was simply doing his job, and yet, Woods made it his life's goal to take the IU leader down.
It's Woods who ultimately causes Alvin Olinksy (Elias Koteas) to get locked up and killed, in season 5, and for that, he places on the list. Not a criminal per say, but close.