Granted, while I am aware that she is already listed as such, but I feel like it should be made official. Mostly because that category was added long before the idea of effort posting came along.
What is the work?
Courage the Cowardly Dog was one of my favorite cartoons growing up. The series concerns Courage, the eponymous cowardly dog who was abandoned as a pup. Until one day, he was found by a Scottish woman named Muriel Bagge who raised him as her own. Now supernatural oddities and monsters come by so Courage has to defend his home from them.
Who is she? What has she done?
Like I mentioned, Muriel is a sweet old Scottish woman, arguably one of the most kind characters in the show. Years ago, she found Courage alone in a garbage dumpster sometime after the Cruel Veterinarian sent Courage's parents into space. Christening him Courage, Muriel then took him home and raised him almost as if he were her son. For the most part, Muriel would serve as the dutiful caretaker who was also ironically married to one of my most hated characters Eustace Bagge. But it's shown that she genuinely does somehow love him despite his faults such as him valuing money over her or using her as bait in a few episodes, or the fact that he often views her as a slave to service him. When Eustace was kidnapped by the Queen of the Black Puddle in the titular episode, she cries over his disappearance thus compelling Courage to rescue him even though he didn't care too much for the farmer.
Muriel can be best described as someone who was selfless who never asked for much in return and was also known to be very hospitable with others. One highlight is the episode "The Hunchback of Nowhere" where she and Courage are the only two characters that display any bit of kindness to the Hunchback by inviting him to breakfast for instance or giving him her husband's raincoat. Really, her kindness played a part in one episode where she got her kindness extracted from her by a brain-like alien. I could provide several examples of Muriel's kindness and good heart, but that'd take all day.
Goodness Zone/Corrupting Factors
Not much in the way of corrupting factors. As I have stated, there was an episode where Muriel became meaner and abusive towards Courage, but it makes sense in universe as to why that was: she had her kindness extracted from her, and she returns to normal when it is returned to her. So she quite literally wasn't being herself at that moment. Other episodes see her hitting Eustace with a rolling pin. However, this is often because Eustace deliberately spooks Courage which results in him getting karmically struck. Aside from that, it is made clear that she loves Eustace, and he reciprocates it in his own ways. Muriel gets transformed into a little girl and became more mischievous, but again, it was more because she wasn't being herself at the time so I wouldn't hold that against her.
Courage literally goes through sheer hell to ensure that Muriel gets out unscathed. The episode "Queen of the Black Puddle" makes it clear that even if Courage disliked Eustace, he was willing to continue to be tormented by him because he loved Muriel that much.