Gwallog ap Llaennog was a hero of the Hen Ogledd

Hen Ogledd

Yr Hen Ogledd is a Welsh term used by scholars to refer to those parts of what is now northern England and southern Scotland in the years between 500 and the Viking invasions of c. 800, with particular interest in the Brythonic-speaking peoples who lived there.The term is derived from heroic...

 and probable 6th century king of the sub-Roman

Sub-Roman Britain

Sub-Roman Britain is a term derived from an archaeological label for the material culture of Britain in Late Antiquity: the term "Sub-Roman" was invented to describe the potsherds in sites of the 5th century and the 6th century, initially with an implication of decay of locally-made wares from a...

 state of Elmet

Elmet

Elmet was an independent Brythonic kingdom covering a broad area of what later became the West Riding of Yorkshire during the Early Middle Ages, between approximately the 5th century and early 7th century. Although its precise boundaries are unclear, it appears to have been bordered by the River...

 in the Leeds

Leeds

Leeds is a city and metropolitan borough in West Yorkshire, England. In 2001 Leeds' main urban subdivision had a population of 443,247, while the entire city has a population of 798,800 , making it the 30th-most populous city in the European Union.Leeds is the cultural, financial and commercial...

 area of modern Yorkshire

Yorkshire

Yorkshire is a historic county of northern England and the largest in the United Kingdom. Because of its great size in comparison to other English counties, functions have been increasingly undertaken over time by its subdivisions, which have also been subject to periodic reform...

.

He joined a group of Brythonic

Britons (historical)

The Britons were the Celtic people culturally dominating Great Britain from the Iron Age through the Early Middle Ages. They spoke the Insular Celtic language known as British or Brythonic...

 kings, including Urien Rheged

Urien

Urien , often referred to as Urien Rheged, was a late 6th century king of Rheged, an early British kingdom of the Hen Ogledd . 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...

, Rhydderch Hael

Riderch I of Alt Clut

Riderch I , commonly known as Riderch or Rhydderch Hael , was a ruler of Alt Clut and the greater region later known as Strathclyde, a Brittonic kingdom that existed on the valley of the River Clyde in Scotland during the British Sub-Roman period...

 and Morgant Bwlch

Morcant Bulc

Morcant Bulc was a Brythonic prince, probably a king, from Northern Britain, during the period between the end of the Roman Empire and the establishment of an English state during the early Middle Ages....

 of Bryneich, in an attempt to defeat the Angles

Angles

The Angles is a modern English term for a Germanic people who took their name from the ancestral cultural region of Angeln, a district located in Schleswig-Holstein, Germany...

 of Bernicia

Bernicia

Bernicia was an Anglo-Saxon kingdom established by Anglian settlers of the 6th century in what is now southeastern Scotland and North East England....

. This endeavour failed after Urien was slain by Llofan Llaf Difo.

Another tradition asserts that Gwallog later made war against Urien's former kingdom of Rheged

Rheged

Rheged is described in poetic sources as one of the kingdoms of the Hen Ogledd , the Brythonic-speaking region of what is now northern England and southern Scotland, during the Early Middle Ages...

 in concert with Dunod Fawr

Dunod Fawr

Dunod Fawr is a figure known from the Welsh Genealogies believed to have been a noble in the post-Roman Hen Ogledd. Dunod was a son of Pabo Post Prydain and is believed to have succeeded his father as ruler of a small polity somewhere in what is now the North of England, possibly in Lonsdale and/or...

 of the Northern Pennines

Pennines

The Pennines are a low-rising mountain range, separating the North West of England from Yorkshire and the North East.Often described as the "backbone of England", they form a more-or-less continuous range stretching from the Peak District in Derbyshire, around the northern and eastern edges of...

, attacking Urien's sons.

In some sources, Gwallog is given the epithet Marchog Trin, meaning "battle horseman". If his identification as king of Elmet is correct, he was succeeded by his son Ceredig

Ceretic of Elmet

Ceretic of Elmet was the last king of Elmet, a Brythonic kingdom that existed in the West Yorkshire area of Northern Britain during sub-Roman times....

, the last king of Elmet, who was deposed by St. Edwin

Edwin of Northumbria

Edwin , also known as Eadwine or Æduini, was the King of Deira and Bernicia – which later became known as Northumbria – from about 616 until his death. He converted to Christianity and was baptised in 627; after he fell at the Battle of Hatfield Chase, he was venerated as a saint.Edwin was the son...

 of Deira

Northumbria

Northumbria was a medieval kingdom of the Angles, in what is now Northern England and South-East Scotland, becoming subsequently an earldom in a united Anglo-Saxon kingdom of England. The name reflects the approximate southern limit to the kingdom's territory, the Humber Estuary.Northumbria was...

.

Over time, Gwallog evolved into a semi-mythological figure akin to Arthur

King Arthur

King Arthur is a legendary British leader of the late 5th and early 6th centuries, who, according to Medieval histories and romances, led the defence of Britain against Saxon invaders in the early 6th century. The details of Arthur's story are mainly composed of folklore and literary invention, and...

. In the medieval text "Geraint son of Erbin", he is named as one of Arthur's knights and also appears in the Welsh triads

Welsh Triads

The Welsh Triads are a group of related texts in medieval manuscripts which preserve fragments of Welsh folklore, mythology and traditional history in groups of three. The triad is a rhetorical form whereby objects are grouped together in threes, with a heading indicating the point of likeness...

 as one of the "Three Armed Warriors of the Island of Britain" and one of the "Three Battle Pillars of the Island of Britain". Gwallog is also mentioned in the Black Book of Carmarthen

Black Book of Carmarthen

The Black Book of Carmarthen is thought to be the earliest surviving manuscript written entirely or substantially in Welsh. Written in around 1250, the book's name comes from its association with the Priory of St. John the Evangelist and Teulyddog at Carmarthen, and is referred to as black due to...

 poem "Ymddiddan Gwyddno Garanhir a Gwyn ap Nudd" as one of the slain warriors escorted to their graves by Gwyn ap Nudd

Gwyn ap Nudd

Gwyn ap Nudd is a Welsh mythological figure, the king of the Tylwyth Teg or "fair folk" and ruler of the Welsh Otherworld, Annwn. Described as a great warrior with a "blackened face", Gwyn is intimately associated with the otherworld in medieval Welsh literature, and is associated with the...

, the lord of the Welsh Otherworld

Annwn

Annwn or Annwfn was the Otherworld in Welsh mythology. Ruled by Arawn, or much later by Gwyn ap Nudd, it was essentially a world of delights and eternal youth where disease is absent and food is ever-abundant. It later became Christianised and identified with the land of souls that had departed...

.