At least two of Dôn's children also have astronomical associations: Caer Gwydion ("The fortress of Gwydion") is the traditional Welsh name for the Milky Way, and Caer Arianrhod ("The Fortress of Arianrhod") being the constellation of Corona Borealis.
The game's title is a pun on the proverb "To err is human, to forgive divine" by Alexander Pope, whose namesake may have been given to the character Gwydion once it is later revealed who he really is in the game.
According to the Book of Taliesin, he fought alongside Gwydion at the Battle of the Trees, in which he assisted his uncle in enchanting the trees to rise up in battle against Arawn, king of Annwn.
The prized horse of Prince Gwydion, Melyngar is most visible in the first book in the series, The Book of Three.
In the final novel of the series, The High King, Gwydion announces that the Sons of Don must board the golden ships on which they came to Prydain and return to the Summer Country.
He awakes to find his wound treated by none other than Gwydion, the crown prince in Prydain's ruling House of Dôn, who has been traveling to Caer Dallben to consult Hen Wen himself.
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Gwydion captures one by enchantment and slays another, so the horsemen fall back, but a pair of undead footsoldiers remorselessly approach: the Cauldron-Born.
Soon after, Taran and Gwydion separately witness Chief Steward Magg leave the castle to go the beach at night and signal a ship at sea.