Dictionary of National Biography, 1885-1900/Copsi
COPSI, COPSIGE, or COXO, Earl of Northumberland (d. 1067), a thegn noted for his wisdom in council, administered the government of Northumberland under Tostig, the earl, at the time of the Northumbrian revolt of 1065. He lost office at the deposition of his master, and may have shared his banishment, for he is said to have taken part in Tostig's expedition against England in the spring of 1066. After the coronation of William the Conqueror, Copsi, like the other northern lords, made his submission to the new king at Barking. When William was about to visit Normandy, he granted Copsi the earldom of Bernicia, or Northumberland north of the Tyne. This grant involved the deposition of Oswulf, the descendant of the ancient earls. By thus appointing a native as his lieutenant, William hoped to gain the obedience of the yet unconquered north, while Copsi probably looked on his appointment by the Norman king simply as a means of self-aggrandisement. Having gathered an army, he marched northwards and dispossessed Oswulf, who was forced to betake himself to the forests and mountains. Before long, however, the banished earl formed a band of men, like himself of broken fortunes, and came upon Copsi unawares while he was feasting at Newburn on 12 March 1067. The earl fled for refuge to the nearest church. Oswulf's men set the church on fire, and so forced Copsi to come forth. When he came to the door, Oswulf cut off his head. The Normans, who called him ‘Coxo,’ made a hero of him, and William of Poictiers speaks in warm terms of the nobility of his birth and of his fidelity to the king, declaring that his men pressed him to side with his own people against the Conqueror, and that his death was the consequence of his faithfulness. He gave several gifts of land to the church of Durham, and a silver cup, which was there in the time of the writer of the Durham history.
[Symeon's Hist. de Dunelm. Eccl. 37, Historia regum, 204 (Twysden); William of Poictiers, 148, 158 (Giles); Orderic, 506 (Duchesne); Gaimar, 5164 (Mon. Hist. Brit.); Dugdale's Monasticon, i. 235; Freeman's Norman Conquest, ii. 484, iv. 21, 76, 107, 741–4.]