Wilyam Baratheon was an early member of House Baratheon.
Biography
Background
Wilyam was the son of Monica Velaryon and an unnamed son of Orys Baratheon.
Season 1
He is mentioned in his father's entry in The Lineages and Histories of the Great Houses of the Seven Kingdoms.[1]
In the books
In the A Song of Ice and Fire novels, there is no such character.