Who is Gwyn from The Owl Service and what is their importance?

Fifteen-year-old, Gwyn, grew up near Aberystwyth, in the country of Wales in the United Kingdom. He is the son of the Nanny, who looks after the little house in the valley where Alison, Roger and their parents come to stay for a summer holiday, and, as such is brought along to help out his mother with the chores and upkeep of the house.

Gwyn is described as a confident, practical young man, who is necessarily self-reliant. He is known to be quick witted, quick tempered, and often resentful of his mother's expectations.