I make none realistic, I may have some inspired off real life things but that's just me. I'm thinking on making a Peridot character from Steven Universe and my gemsona, but I'm too lazy. But rarely any humanoids rather than gems.
EDIT: Forgot to say how. I make my characters first by listening to a song, then it think of the mood of the song and then just make the song sound like it fits a scenario. Then I imagine a scene with a random character, that's how they begin. Then I imagine their look and personality, how they would react to their surroundings and such. It usually takes weeks of imagining over and over again in order to construct one character.