Constantine of Strathclyde was a 6th-century monarch and saint who ruled the Brittonic kingdom of Alt Clut, a realm later called Strathclyde. As the son of King Riderch Hael, he eventually succeeded his father to the throne. According to hagiographical traditions, he later abdicated his royal position to pursue a religious life as a clergyman. While his historical existence is debated due to a lack of contemporary genealogies, he remains a significant figure in religious narratives associated with the early Christianization of the region.