Many comic villains flit between doing good and evil as if they're options on life's great buffet. While it's endlessly interesting having to guess whether a character will do the right thing, this pales in comparison to one of the most interesting storylines a villain can have - namely, their reformation.
And a surprising number of villains have made this storyline last for good, making their reformation permanent. From heroes who turned good so long ago that you forget they were even evil - like Hawkeye and Plastic Man - to characters like Tomorrow Woman who exist solely to provide an interesting villain reformation, there are endless ways that this kind of storyline can be done, and all of them are equally fascinating.
As much as it's fun to see villains be absolutely terrible, there's something about watching a bad guy redeem themselves that just makes you feel good.
Not only does it make for more three-dimensional and ultimately more human characters, it also comes as a solid reminder that you don't have to be great 100% of the time to become a good person - you just have to want to do good.
10. Clayface (Basil Karlo) - Detective Comics #934
With it being so hard to not feel bad for Clayface - professional actor turned into a spooky mud monster against his will - it was somewhat inevitable that the Batman villain would eventually get his time in the sun.
And that he did, as Detective Comics #934 saw the sympathetic bad guy turned full hero, after he accepted an invitation from Batman to join the Dark Knight's forces. Perhaps the most heartbreaking moment of all of this has to be that Karlo immediately accepts the offer, leaving the tragic implication that he likely would have become good some time before had someone just asked him nicely.
While Karlo was briefly driven back into a monstrous rage by the Monster Men serum, it is worth noting that this isn't his fault, and that when this serum inadvertently cured him, Karlo immediately committed to trying to live a more moral life, egged on by his new inconspicuous appearance.