Ecgfrith (or Egfrith; c. 646 AD–685 AD) was the King of Deira from 664 AD until 670 AD . When his father died he became King of Northumbria from 670 AD until his death. Ecgfrith ruled Northumbria when it was at the height of its power. His reign ended with his defeat at the Battle of Nechtansmere in which he died.