William FitzAldelm, FitzAdelm, FitzAldhelm, or FitzAudelin was a Norman noble from Suffolk or North Yorkshire. He was the son of Adelm de Burgate. He was an important as a courtier and took part in the Norman invasion of Ireland.
In 1165 William FitzAdeline's father Adelm d'Aldfied and his brother Ralph FitzAdeline gave lands at Fountains to the Abbey, which gift was confirmed by Roger de Mowbray. Ralph FitzAdeline held one fee in Yorkshire from Mowbray in 1165, and witnessed a charter by his brother to the Knights Hospitallers.
The manor of Ongar alias Little Ongar, later known as Ashhall alias Nash Hall was held as a marshalship. This marshalship consisted of looking after the prostitutes at the king's court, dismembering condemned malefactors, and measuring the king's 'gallons' and 'bushels'. In 1156 this strange office had been held by William Fitz Audelin, who had received it in marriage with Juliane Doisnel, daughter of Robert Doisnel. The manor of Sherfield Upon Loddon was held by the English Crown till the reign of Henry II, by whom it was granted, before 1167-8, to his marshal William Fitz Aldelin on his marriage with Juliane. William held the manor by the serjeanty of being the king's marshal. The manor of Compton was given by the King from his marriage to Juliane.
It is evident from the latter charter that he accompanied King Henry II in his expedition to Ireland in October 1171. He was sent with Hugh de Lacy to receive the allegiance of Rory, King of Connaught, and on the King's return to England in the next year the city of Wexford was committed to his charge, with two lieutenants under him. In 1173 Pope Adrian's bull granting the kingdom of Ireland to Henry, Laudabiliter, was entrusted to the prior of Wallingford and him to exhibit before the synod of bishops at Waterford. On the death of Strongbow, Lord of Leinster, in 1176, the king appointed him deputy over the whole of that kingdom and granted him the wardship of Isabel, the earl's daughter and heir.