Question: Meirchion Gul was a King of which Brittonic-speaking region of Northern England and Southern Scotland?

full_context: Document 1: Kingdom of Strathclyde: Strathclyde (lit. "Strath of the River Clyde"), originally Cumbric: Ystrad Clud or Alclud (and Strath-Clota in Anglo-Saxon), was one of the early medieval kingdoms of the Britons in "Hen Ogledd" ("the Old North"), the Brythonic-speaking parts of what is now southern Scotland and northern England. The kingdom developed during the post-Roman period. It is also known as Alt Clut, a Brittonic term for Dumbarton Castle, the medieval capital of the region. It may have had its origins with the Brythonic Damnonii people of Ptolemy's "Geography".
Document 2: King of the Britons: The title King of the Britons (Latin "Rex Britannorum") was used (often retrospectively) to refer to the most powerful ruler among the Celtic Britons, both before and after the period of Roman Britain up until the Norman conquest of England. The Britons were the Brittonic-speaking peoples of what is now England, Wales, and southern Scotland, whose ethnic identity is today maintained by the Welsh, Cornish and Bretons.
Document 3: Meirchion Gul: Meirchion Gul was probably a late 5th-century king of Rheged, a Brythonic realm in the area of sub-Roman known as the "Hen Ogledd" (in the North of England and Southern Scotland today).
Document 4: English language in Northern England: The English language in Northern England has been shaped by the region's history of settlement and migration, and today encompasses a group of related dialects known as Northern England English (or, simply, Northern English in the United Kingdom). Historically, the strongest influence on the varieties of the English language spoken in Northern England was the Northumbrian dialect of Old English, but contact with Old Norse during the Viking Age and with Irish English following the Great Famine have produced new and distinctive styles of speech. Some "Northern" traits can be found further south than others: only the northernmost accents of Northumberland and Tyneside retain the pre-Great Vowel Shift pronunciation of words such as "town" ( , ""toon""), but all northern accents lack the – split, and this trait extends a significant distance into the Midlands.
Document 5: Bonedd Gwŷr y Gogledd: Bonedd Gwŷr y Gogledd (English: The Descent of the Men of the North ) is a brief Middle Welsh tract which claims to give the pedigrees of twenty 6th century rulers of the Hen Ogledd, the Brittonic-speaking parts of southern Scotland and northern England. It is attested in a number of manuscripts, the earliest being NLW, Peniarth MS 45, which has been dated to the late 13th century. The text may have been composed in the 12th century. The historicity of much of the information is spurious or in doubt. Although certain parts are in agreement with the earlier Harleian genealogies, the text represents a substantial revision seeking to integrate the branches of many rulers and heroes who are prominent in other traditions, such as the Rheged prince Llywarch Hen.
Document 6: Kings of the Angles: The Angles were a dominant Germanic tribe in the Anglo-Saxon settlement of Britain, and gave their name to the English, England and to the region of East Anglia. Originally from Angeln, present-day Schleswig-Holstein, a legendary list of their kings has been preserved in the heroic poems "Widsith" and "Beowulf", and the "Anglo-Saxon Chronicle".
Document 7: Music of Northumbria: Here Northumbria is taken to mean Northumberland, the northernmost county of England, and County Durham. This area, together with Tweeddale, was the ancient British tribal kingdom of Bernicia (Bryneich) and is notable for the stable ancestry of its present indigenous population, which has been identified by DNA analysis to be an offshoot of the group Scotland, Cumbria and the North of Ireland, but not so closely related to the other peoples of the UK. The area was the core of the outstanding artistic culture that developed during the Northumbrian Golden Age of the 7th and 8th centuries; it would be unwise to suggest that the area did not have a flourishing musical culture at that time, or that it was not of similar sophistication - Bede makes reference to the playing of the harp. The traditional music of this area may be a tangible legacy of the Bernicians - given that little is known of the antiquity of Northumbrian music; though traditional Northumbrian instruments would have had their limitations. However, much surviving early modern Northumbrian music is similar in form to the music of the Scottish Lowlands, so Northumberland's position on the cultural frontier between England and Scotland has played a significant role. The modern era has seen Northumbrian traditional music artificially pigeon holed into national divisions, into which Northumbrian music simply will not fit. Likewise, the crude assumption that the font of all music of substance was in the west and north of the British isles has undermined considered appreciation of the local repertoire.The region possesses a distinctive style of folk music with a strong and continuing tradition. The region is particularly noted for its tradition of border ballads, the Northumbrian smallpipe (a form of bagpipe unique to north-east England) and also a strong fiddle tradition in the region that was already well established in the 1690s. Northumbrian music is characterised by considerable influence from other regions (and vice versa), particularly southern Scotland and other parts of the north of England. Irish tunes are also much played in the region, as they are elsewhere. There has been a continuous tradition of traditional and distinctive Northumbrian styles since the 18th century – there have also been 'revivals' in the late nineteenth century and again in the mid-twentieth. More recently, Northumbrian folk music, and particularly the use of the Northumbrian pipes, has become one of the liveliest and most widely known forms of folk music in Britain.
Document 8: Coel Hen: Coel (Old Welsh: "Coil") or Coel Hen ("Coel the Old") is a figure prominent in Welsh literature and legend since the Middle Ages. Early Welsh tradition knew of a "Coel Hen" (Coel the Old), a "circa" Fourth Century CE leader in Roman or Sub-Roman Britain and the progenitor of several kingly lines in the Hen Ogledd ("the Old North"), the Brittonic-speaking part of northern England and southern Scotland. Later medieval legend told of a Coel, apparently derived from Coel Hen, who was the father of Saint Helena and the grandfather of Roman Emperor Constantine the Great. Other similarly named characters may be confused or conflated with the Welsh Coel. The legendary "King Coel" is sometimes supposed to be the historical basis for the popular nursery rhyme "Old King Cole", but this is unlikely.
Document 9: Pictish language: Pictish is the extinct language, or dialect, spoken by the Picts, the people of eastern and northern Scotland from the late Iron Age to the Early Middle Ages. There is virtually no direct attestation of Pictish, short of a limited number of geographical and personal names found on monuments and the contemporary records in the area controlled by the Kingdom of the Picts. Such evidence, however, points to the language being closely related to the Brittonic language spoken prior to Anglo-Saxon settlement in what is now southern Scotland, England and Wales. A minority view held by a few scholars claims that Pictish was at least partially non-Indo-European or that a non-Indo-European and Brittonic language coexisted.
Document 10: Rheged: Rheged (] ) was one of the kingdoms of the "Hen Ogledd" ("Old North"), the Brittonic-speaking region of what is now Northern England and southern Scotland, during the post-Roman era and Early Middle Ages. It is recorded in several poetic and bardic sources, although its borders are not described in any of them. Some modern scholars have suggested that it included what is now Cumbria in North West England and possibly extended into Lancashire and Scotland. In some sources, Rheged is intimately associated with the king Urien Rheged and his family. Its inhabitants spoke Cumbric, a Brittonic dialect closely related to Old Welsh.
Document 11: Hen Ogledd: Yr Hen Ogledd (] ), in English the Old North, is the region of Northern England and the southern Scottish Lowlands inhabited by the Celtic Britons of sub-Roman Britain and the Early Middle Ages. Its denizens spoke a variety of the Brittonic language known as Cumbric. The Hen Ogledd was distinct from the parts of northern Britain inhabited by the Picts, Anglo-Saxons, and Scoti as well as from Wales, although the people of the Hen Ogledd were the same Brittonic stock as the Picts, Welsh and Cornish, and the region loomed large in Welsh literature and tradition for centuries after its kingdoms had disappeared.
Document 12: Kingdom of Northumbria: The Kingdom of Northumbria ( ; Old English: "Norþhymbra rīce" , "kingdom of the Northumbrians") was a medieval Anglian kingdom in what is now northern England and south-east Scotland, which subsequently became an earldom in a unified English kingdom. The name reflects the approximate southern limit to the kingdom's territory, the Humber estuary.
Document 13: Urien: Urien , often referred to as Urien Rheged or Uriens, was a late 6th-century king of Rheged, an early British kingdom of the "Hen Ogledd" (northern England and southern Scotland). His power and his victories, including the battles of Gwen Ystrad and Alt Clut Ford, are celebrated in the praise poems to him by Taliesin, preserved in the "Book of Taliesin". He became the "King Urien of Gorre" of later Arthurian legend and his son Owain mab Urien was later known as Ywain.
Document 14: Kingdom of Gwent: Gwent (Old Welsh: "Guent" ) was a medieval Welsh kingdom, lying between the Rivers Wye and Usk. It existed from the end of Roman rule in Britain in about the 5th century until the Norman conquest of England in the 11th century. Along with its neighbour Glywyssing, it seems to have had a great deal of cultural continuity with the earlier Silures, keeping their own courts and diocese separate from the rest of Wales until their conquest by Gruffydd ap Llywelyn. Although it recovered its independence after his death in 1063, Gwent was the first of the Welsh kingdoms to be overrun following the Norman conquest.
Document 15: Northumbrian dialect: Northumbrian was a dialect of Old English spoken in the Anglian Kingdom of Northumbria. Together with Mercian, Kentish and West Saxon, it forms one of the sub-categories of Old English devised and employed by modern scholars.
ground_truth: Rheged