The robot named Rex had been bought as a companion for Paul when the Simpsons decided to pioneer on Ganymede, a moon of Jupiter...a rough, dangerous satellite where a small boy needed a strong, intelligent robot to protect him. By the time Paul is sixteen, they are inseparable. Robots, of course, have a personality leeway that gives each one a certain individuality within its pattered capacities -- and Rex had a wonderful personality, with a logic...