To Heir is Human by Annette Childs

The prologue printed in the manual for King's Quest 3 by Annette Childs...

King's Quest III: To Heir is Human by Annette Childs
A long, long time ago, when magic was the only science known to man, there dwelt in the land of Llewdor a wizard named Manannan. He was very learned in all matters of the heavens and earth.

Of great age, Manannan presented a frail appearance, as though his skin were made of bleached and weathered parchment. Manannan's impression of fragility lasted only until one looked into his coal-black eyes, which burned with a strange fire. This was, indeed, a powerful wizard.

Although he was powerful, and capable of conjuring up vast armies of spirit servants to sweep his hearth, prepare his meals and other menial tasks with which he would not soil his hands, this solution to his everyday needs was not satisfactory to him. For he liked his solitude, and didn't want a lot of spirits (who besides all else, are quite inquisitive and mischievous) cluttering up his house. Instead, he impressed a very young boy to do his bidding, taking the lad when he was only a year old, so he would have no memories to tug at him in the years to come.

Unfortunately for Manannan, boys grow up and become adventuresome young men. As his slave grew in stature and in strength, Manannan was irritated to find him poking around in areas of the house where he didn't belong. Or he would climb down the narrow path leading to Manannan's mountaintop retreat to explore the surrounding countryside. Even punishment did not stop him for long.

One day, when his slave was 18 years of age, the wizard found him practicing magic spells. This was the last straw!

"YOU!" Manannan screamed. "You have read my books of spells and plundered my supplies of powders and potions. You have even ventured into Llewdor again, against my expressed command, for nowhere else could you have gathered some of these ingredients!

"You think you will win your freedom with these tricks?" the wizard sneered. "You shall see your mistake! You have earned only your own demise!" And with that, Manannan raised his hands menacingly.

Suddenly the earth began to shake. And his slave was no more. Only a small pile of ashes remained where he had stood.

"Next time, I won't make the same mistake," Manannan snarled. "I'll never let any of my slaves reach manhood. I'll have no more accidents."

And so the years passed. Manannan went out and found another small boy to be his slave. He stole him from a country some distance from Llewdor, to direct suspicion away from himself. Manannan was more careful with this child, and watched him closely. The wizard punished the boy severely when he caught him away from the house. And he made sure the boy didn't get his hands on even any ordinary items that might be transformed into magic charms or potions. On the whole, Manannan didn't have much trouble with him, but still, on the lad's 18th birthday, the wizard zapped him out of existence.

"It's a nuisance, having to train a slave all over again," he mumbled complainingly. "But it's better than having trouble like the last time."

And so he went on, every 17 years kidnapping a small boy from his loving parents, then slaying him on the 18th anniversary of his birth. (Occasionally the cycle was shortened slightly, when he unfortunately chose a precocious child that learned too much before his 18th year.)

And time went on...