Urien ap Cynfarch Oer (Welsh pronunciation: [ˈɨ̞riɛn ap ˈkənvarχ oːɨ̯r]) or Urien Rheged (Welsh pronunciation: [ˈɨ̞riɛn ˈr̥ɛɡɛd], Old Welsh: Urbgen or Urbagen, Old Welsh pronunciation: [ɨ̞rβ(ə)ˈɣɛn]) was a powerful sixth-century Brittonic-speaking figure who was possibly the ruler of the territory or kingdom known as Rheged. He is one of the best-known and best documented of the British figures of the Old North. His kingdom was most likely centred around the Solway Firth. According to the section known as the "Northern History" of the Historia Brittonum (c. 829–30 AD), Urien gained a decisive advantage in a conflict against the Anglo-Saxons in northern Britain while leading an alliance with three other kings: Rhydderch Hen, Gwallog ap Llênog, and Morgan. The alliance led by Urien penned the Anglo-Saxons in at Lindisfarne, though this siege came to an abrupt end when Urien was murdered on the orders of his erstwhile ally Morgan.
The most secure evidence for his existence comes the Historia Brittonum and eight praise-poems in Middle Welsh orthography dedicated to him surviving in a fourteenth-century manuscript. Despite their being found in later orthography, the poems may possibly reflect early material, even material contemporaneous to Urien. One of these poems is explicitly attributed to the famed poet Taliesin in the manuscript. The "Northern History" in the Historia Brittonum also roughly synchronises Taliesin's career to the reign of Ida of Bernicia (547 × 549). Some of the Beirdd y Tywysogion (c. 1100–1283) also allude to this strong association between Taliesin and Urien. The panegyric attributed to Taliesin concerning Urien is particularly significant because if it truly originates in the sixth century it, together with the poetry attributed to Aneirin, would be the earliest vernacular post-Classical European literature.