Donald m. Proto-Celtic *dumno- 'world' + Proto-Celtic *val 'rule'.
The name of a 7th C king of Dál Riata, a 7th C high king of Ireland, an 8th C Irish saint, an 8th C high king of Ireland, two 9th C kings of the Picts, and 11th C king of the Scots, and an 11th-12th C high king of Ireland.
This name has historically always been one of the most popular names in Ireland.