Anglo-Saxon king of the Northumbrians from 670 who ultimately lost his wars against the Mercians on the south and the Picts on the north.

Ecgfrith was the son of King Oswiu and nephew of St. Oswald and a generous supporter of his kingdom's great monasteries. By 674 he defeated a south English coalition under Mercian leadership and annexed the region of Lindsey. In 678, however, Ecgfrith was defeated near the River Trent by King Aethelred of Mercia. During an invasion of Pictish territory, he was killed at a place called Nechtanesmere (Duin Nechtain), and his army was destroyed.