 Oslac ( fl . 966 – 975 ) is regarded as the first ealdorman ( or earl ) of York and its dependent territories . These included but may not have been limited to the southern half of Northumbria . His background is obscure because of poor source documentation . The latter has facilitated disagreement amongst historians regarding his family and ethnicity . It is not even certain that Oslac was a name .
 sierpiel ( Oslac ) is a Germanic name . It may be a personal name or a byname . It is also a word meaning 'osier' . Oslac's name is recorded in the Anglo-Saxon Chronicle in