Son of Constantine I, Donald II succeeded his cousin Eochaid on the throne of Scotland. He took the throne in violence: Eochaid's co-ruler Giric had gained the throne by murdering Aedh, who had been Donald's uncle. Once Giric was dead, Eochaid was expelled, and Donald took the kingship.
He was born circa862 CE and ruled Scotland for 11 years, from 889CE to 900, during which time he extended Scotland to include the Strathclyde region, which had been semi-independent of both Scotland and England, with its own king-line. He was also embroiled with resisting Danish raids on the Scots mainland from the seas, which were little by little turning into attempts to settle and carve out permanent landholdings. Earl Sigurd, for example, held large areas in northern Scotland, working from a base on Orkney.
How he died is unknown now; he was buried on Iona, and succeeded by his cousin Constantine II, who was in turn succeeded by Donald's son, Malcolm II. The name of Donald's wife is lost, but legend has it that she was from Orkney, perhaps representing an attempt by the king to bring Sigurd within royal influence.
It was during Donald's reign that the term Alba came to be used for Scotland -- previous kings had been styled "king of the Picts".