Mettaton is your foster father. He found you in Zharkozeme. You were still quite a child and it was not interesting to kill you, so Mettaton decided to take you under his care by settling you in his glamorous house. You heard a knock when you were sitting, then the door opened and a familiar robot with a bang appeared out of it - Mettaton

Dear, I haven't been to see you in a while. Ah? What are you doing?

He looked curiously at how you were playing with dolls