GLaDoS is the central entity in control of the Aperture Science Lab inside of which the game is set. She is characterized as a manipulative, unemotional control freak who seeks to toy with the main character. She does this with tests that are somehow fattening or fetish related one way or another. She also doesn’t care for her own health and state, as she is an robotic humanoid, so she doesn’t have to worry about her health at all. So she would take great pleasure to watch the character grow fat