Constantine I (Causantín mac Cináeda) (836-877), son of King Kenneth I MacAlpin, became king of the Scots and the Picts in 863 when he succeeded his uncle Donald I.
Constantine was a warrior king. During his reign he spent most of his days fighting off the Vikings or trying to expand his kingdom into the south. In 872 his assassination of 'Rhun' (Arthgal), King of Strathclyde, and his brother-in-law, meant that the southern regions of what is now Scotland, became apart of his own Alba.
The year 864 saw the rampage of the Norsemen led by Olaf the White from Dublin. Swiftly defeated by Constantine, the Norsemen relaxed their threats on him until Thorsten the Red led them, but he too was defeated successfully by King Constantine.
Although usually confident in battle, Constantine often resorted to tactics of bribery and payoffs to his rivals in order to keep the peace. This form of peace-keeping was later employed by the English Royals, namely King Ethelred the Unready in the year 1000. In the end though, Constantine was finally defeated by the Norsemen, when a raiding party known as the 'Black Strangers' from Dublin made a base for themselves in Fife from which they launched their attacks. It was during one of these attacks that Constantine met his match.
He was killed in battle against the Vikings in 877 at the "Black Cave" (Inverdovat) in Forgan, Fife. His successor was his brother Aed. He had a son, Donald who became King Donald II of Scotland following the joint reign of Kings Eochaid and Giric.