Gwydion

Gwydion is a slave boy in KQ III, where we find him in a home on top of a mountain.

Background
He was kidnapped soon after his birth by the wizard Manannan himself, from the royal nursery of Daventry near the shores of Lake Maylie. Manannan renamed him Gwydion. Manannan had a cat (a previous rival of Manannan's that got the cat cookie treatment) who doesn't like Gwydion. Gwydion was forced to work for Manannan as a slave. He was nearing his 18th birthday and he knew that he was soon going to die, so he prepared his plan of escape. He knew that Manannan was extremely punctual and his life ran like clockwork. So he knew he could sneak around at certain times and learn things around the country of Llewdor and within Manannan's home. Eventually, he learned different spells during his secret travels around the land of Llewdor, and turned Manannan into a cat (using the aforementioned cat cookie recipe) and escaped. He met the Oracle of Llewdor who gave him some information about his past, and he learned about his sister, and the danger she was in. He booked passage on a ship bound for Daventry, but the crew turned out to be pirates, and he was captured by them, but was able to escape them also, through the use of one of his learned spells. He was able to learn more about his past from animals in Llewdor including his name, Alexander, and the names of his family. Eventually he made it to Daventry where he learned many more interesting pieces about his past. Including more about himself, and his name finally being confirmed. He fought the Three-headed Dragon killing it with a spell, which saved his sister. He showed her his birthmark to prove who he was. He still thought of himself as Gwydion many years after his return to Daventry, and treated the name Alexander as if it was just another identity that he wears much like a cloak. His full name became Alexander-Gwydion.

Behind the scenes
Gwydion in Welsh mythology was the name of a son of the goddess Don.

There is some implication in the King's Quest Companion, 2nd Edition, that Gwydion is a name that Manannan gives to all his slaves.