Stars is the Outertale version of Gaster according to Bun-bunmuse. He and Fell are currently available for questions on Bun-bun's Tumblr.
He is mostly calm, except if someone is helplessly ignorant or if he has sugar. He is open-minded, well-mannered, gentlemanly and careful. He has never seen a human, and states he's heard they're quite complex creatures. He is fatherly, mostly to Wingding, but can only do so much. If Swap is sick, he is a good stand-in for him.