The families with a "Fitz-" prefix go back to some of the supporters and soldiers of William the Conqueror, the first Norman king of England.  It is an Anglican adulteration of the French phrase of "fils de" meaning "son of". This is typical naming technique found in Scandinavia and Scandinavian settlements such as in Scotland or Ireland where "Mac" is used.  This prefix identifies the family with associations to early Scandinavian invaders and settlements of Normandy, France and England. Normandy was the home of Viking families and supporters of the Edward the Confessor, Harold and William the Conqueror.

 Earliest connections go back to some of the first Danish kings,  Gorm the Old of about 936 was succeeded by his son, Harald Bluetooth. Harald went off each season for raiding and pillaging from Denmark to Normandy.[wikipedia.com]

Roger Fitznicholas is one of the many heirs of one of the longest unbroken genealogical lines in England outside of royalty. The Berkeley family and castle begins in about 1066.  The Berkeley castle is one of the oldest in England outside of the Tower of London.