OSLAC (fl. 966), Northumbrian earl, witnessed a charter as dux or earl in 963 (Kemble, Codex Dipl. No. 604; Green, Conquest of England, p. 316 n.) In 966 King Eadgar [q. v.] divided the Northumbrian earldom, over the whole of which Oswulf or Osulf had ruled since 953 or 954, and appointed Oslac earl of the portion described by Symeon of Durham as York and its dependent lands ('fines'), that is, of the ancient kingdom of Deira (Historia Regum ap. Symeonis Opera, ii. 94, 197, 382). The connection between Northumbria and the southern parts of England seems to have been drawn closer during Oslac's term of office. The Danelaw was becoming anglicised, and Oslac appears several times as witnessing charters of Eadgar, though not nearly so often as would have been the case had he held a more southern earldom, and he no doubt had a large measure of independence. Eadgar, indeed, expressly recognised the right of the northern people to their own laws and customs, decreeing that 'secular rights should stand among the Danes with such good laws as they best might choose' (Ancient Laws, i. 273). To his more or less independent position Oslac probably partly owed the reverence with which he was regarded. He is styled the 'great earl' (A.-S. Chronicle) and the 'magnificent earl' ('dux magnifies,' Florence, an. 976). On the death of Eadgar in 975 Oslac was banished from the kingdom — unjustly according to the opinion of the monastic party — and went over sea. His banishment, which is lamented in a song inserted in the 'Anglo-Saxon Chronicle' (an. 975), seems to have been connected with the predominance of Ælfhere, the Mercian earl, the enemy of the monks, but was perhaps due to political rather than ecclesiastical exigencies. After his banishment North umbria was again united into a single earldom under Waltheof, the father of Uchtred, who was, it may reasonably be conjectured, of the house of Oswulf.
[Sym. Dunelm. ii. 94, 197, 382, Anglo-Saxon. Chron. ann. 966, 975, Hist. Rames. p. 50 (all in Rolls Series); Flor. Wig. i. 145 (Engl. Hist. Soc.); Kemble's Codex Dipl. Nos. 543, 555, 556, 562, 566, 567 (Engl. Hist. Soc.); Thorpe's Anc. Laws and Inst. i. 273; Green's Conquest of England, pp. 316, 325, 354; Freeman's Norman Conquest, i. 292.]