First This is the first drawing of done of Fisk. Originally a human, Fisk contracted a deadly magical illness as a child. Lydia the witch was able to cure him, but in doing so left his form unstable. He shapeshifts very easily; without additional safeguards he will change form without even meaning to. He spends so much time as various animals that he doesn't consider himself to be any species in particular; just a shapeshifter. Lydia saw fit to cast a spell that puts Fisk's form under her control. The relationship between the two is a strange one; to Lydia, Fisk is some combination of pet, servant, and adopted son.
I frequently imagine him in the form of a dog. Here, a teenage Fisk is angry that Lydia turned him into a dog to stop him from sneaking out to see a girl.