July 24/25, 759: King Oswulf of Northumbria killed by his own men
It would be a gross oversimplification that it was never an easy nor a safe job to be king of the Northumbrians. The other Anglo-Saxon kingdoms were no picnic either, and the flowering of learning in Northumbria that produced beautiful manuscripts like the Lindisfarne Gospels and scholars like Bede and Alcuin is at least as important. But the Northumbrians kept the fluid "if we don't like this king we'll replace him" approach much longer than other kingdoms, from the two subkingdoms of Deira and Bernicia alternately taking each other over in the seventh century, to the merry-go-round by which the Northumbrians alternately accepted King Eadred of England, Erik Bloodaxe, and another Viking prince, Olaf Cuaran, in the mid-tenth century.
The most notoriously unstable period was the second half of the eighth century, and the murder of Oswulf is the stroke that began it. Oswulf's father Eadberht had ruled Northumbria for twenty years (737-58), and then retired to Lindisfarne, naming his son Oswulf as his successor. But the succession of the son was nothing like automatic in Anglo-Saxon England before the tenth century. Offa of Mercia had his son Ecgfrith consecrated while Offa still lived to ensure his succession, but Ecgfrith only lived 141 days after his father died in 796. Alfred went to some lengths to ensure that his son (Edward the Elder) would succeed him in 899, but Edward still had to fight off a bid for power from Æthelwold, Alfred's brother's son. And although Oswulf Eadberht's son became king of the Northumbrians, he was killed "by the men of his household" a year later. And most of the Northumbrian kings for the next fifty years (there were seven of them) only ruled for a few years before being driven out or killed.
Review the history, 757-806