It depends on who you’re asking. Robert McKee talks about the center of good, a good trait within anyone. Only when a reader sees the center of good do they open up to identify with that character.

Animal torturers are believable in that they can indeed exist. It’s hard for the vast majority of people to identify with them. However, if a writer shows us that an animal torturer is very kind to their daughters, we will still despise them, but we may also be able to identify more readily with them.

There’s the rub though, especially for fantasy writers it’s a razors edge to make a character that is believable on their own that also interacts with a fantastical setting in a natural way. It’s more than just slapping a hobby or two on them and calling them fleshed out, there’s a trick to it that I just haven’t cracked yet, no matter how many times I read the masters of the craft.