Her kingdom wasn't vast. Her subjects weren't numerous. But Cat inspired the sort of devotion in her people that would make Earth's lesser monarchs sick with envy. Cat, the beloved feline and supreme ruler of our household, died peacefully Wednesday at a veterinary facility in Rio Linda, California. She was 18 years old. It's difficult for most Americans to understand the grief that strikes when a beloved monarch dies. Our family now understands it all too well. Apart from small gestures of affection, we subjects were generally forbidden to shower Cat with our love. Even so, she would never let us feel even for a moment that we were unloved. Cat watched over us all. She would appear as if by magic, always there to provide comfort when one of her subjects needed her. Cat had a way of knowing you could use some company before you even realized it yourself. I joined the royal family by marriage, of course, to Cat's human servant. "We're a package deal,"