Constantine II was the son of Aed. He ruled for over 40 years, repelling Norse raids and launching a series of invasions of Northumbria.
In an attempt to establish a more stable relationship with the Norsemen of Ireland, Constantine married his daughter to Olaf III Guthfrithsson in the 930s. This dynastic marriage may have also had the intention of checking the advance of Wessex in northern England - if so, it failed.
Constantine was finally defeated in 937 by the Anglo-Saxon king Athelstan at the Battle of Brunanburh, where one of his sons was killed.
He abdicated in 943, entered a Culdee monastery in St Andrews, Fife and died in 952.