King of Northumbria (796)
Osbald had long been a supporter of Aethelred against the rival claims of the descendents of Eadberht; he was active in resisting Aelfwald, Eadberht's grandson when he seized the throne in 779 before being driven into exile and was generally believed to have had a hand in the assassination of Aelfwald in 788.
He returned to Northumbria in 790 when Aethelred returned to power and served as patricius to Aethelred from 793 onwards. Therefore after the assasination in 796 of Aethelred, Osbald was the obvious candidate amongst the party of Aethelred to succeed him. Or as Simeon of Durham put it, he was "appointed to the kingdom by some nobles".
Osbald however holds the record for the shortest lived Northumbrian king; he lasted for a mere 27 days before being driven out of power.
He fled to Lindisfarne where he seems to have had some supporters and from there onwards into exile (together with a few monks) for the second time in Pictavia. Osbald seems to have entertained notions of attempting a return, but Alcuin disuaded him urging him not to "pile sin upon sin by ravaging the land". Osbald therefore became a monk himself. He died in 799 and was buried at York.
A Biographical Dictionary of Dark Age Britain by
Ann Williams, Alfred P Smyth and DP Kirby (Seaby 1991)
Historia regum Anglorum et Danorum
by Simeon of Durham