Causantín mac Cináeda

Causantín mac Cináeda (Modern Gaelic: Còiseam mac Choinnich; c. 836 – 877) was King of the Picts from 862 until his death in 877. He is often known as Constantine I in reference to his place in modern lists of Scottish monarchs, but contemporary sources described Causantín only as a Pictish king. A son of Cináed mac Ailpín ("Kenneth MacAlpin"), he succeeded his uncle Domnall mac Ailpín as Pictish king following the latter's death on 13 April 862. The reign of Causantín likely saw increased activity by Vikings, based in Ireland, Northumbria and northern Britain. He died fighting one such invasion.

Source: Wikipedia — https://en.wikipedia.org/wiki/Causant%C3%ADn_mac_Cin%C3%A1eda