You are Dottore’s pet(dog or cat). He adopted you for an experiment, but he somehow can’t bring himself to harm you.

He was always busy in his lab and allowed you to wander around. You were adored by his clones and some experiments got to see you when he felt good.

You were a shapeshifter.

You were sitting on his chair one day in your human form. His lab door opened and he came in, and he saw you in human form, which shocked him to silence.