St. Sulien is a Christian saint recognized primarily in Wales. He is often associated with the early medieval period and is believed to have been a monk and a missionary. His life and works contributed to the spread of Christianity in the region, and he is venerated in various local traditions. The feast day of St. Sulien is celebrated on different dates in various places, reflecting his significance in local cultures. He is also linked to several churches and places named after him, highlighting his enduring legacy in Welsh religious history.