From Wikipedia:
Llywarch Hen (meaning 'Llywarch the Old') was a 6th-century prince and poet of the Brythonic kingdom of Rheged, a ruling family in the Hen Ogledd or 'Old North' of Britain (modern southern Scotland and northern England). Along with Taliesin, Aneirin, and Myrddin, he held to be one of the four great bards of early Welsh poetry. Whether he actually wrote the poems attributed to him is unknown, and most of what is known about his life is derived from early medieval poems which may or may not be historically accurate. Llywarch Hen was the son of Elidurus, chief of Argoed (in the Rheged region, later Cumberland). In the genealogy known as "Bonedd Gwŷr y Gogledd (The Descent of the Men of the North)" he is listed as a descendant of Coel Hen (King Cole), and is first cousin to King Urien Rheged. It is thought that he may have been a monarch himself, with Urien ruling northern Rheged, and Llwarch ruling the south.
In his youth, he is said to have fought by the side of the brave Gereint, at the Battle of Llongborth. After the battle, he attached himself to the court of Urien, where he "lived bravely, clothed himself sumptuously, did not spare the ale and mead, and was blessed with 24 sons." These sons are mentioned in the poem Canu Llywarch Hen, although various sources list as many as thirty-nine, plus a few daughters After the fall of Urien, Llywarch was given the task of returning to Rheged with Urien's severed head.
The kingdom fell to Urien's son Owain, who was slain at the Battle of Catraeth, along with almost the entire host of Britons, including all of Llywarch's sons. His friends and family all dead, he is advised to flee to court of Cynddylan in the Powys.
When Cynddylan was slain in battle, Llywarch was left friendless and destitute, with nothing but the milk from a single cow to support him. According to legend, he lived in a hut at Aber-Ciog (now called Dol-Giog), alone with his harp, composing his poems (which would have been sung). At this point, a monk associated with Llanfor in Meirionydd, near Llyn Tegid in Gwynedd is said to have taken pity on him, converted him, and witnessed his happy death.
Near this site, there is a mound known was known as Pabell Llywarch (Llywarch's Tent), and further south lies Clwadd Llywarch Hen (Llywarch Hen's Dyke). The Bonedd lists his date of birth c. 534, and his death c. 608, meaning he would have been around 80 years old at the time of his death, in keeping with his reputation as Llywarch "the old."
However, some sources list different birth and death dates, with claims of his age reaching 105, or even 150 years. His life was the subject of a presumed lost saga of which only the poetry, a series of Englynion, survives. The words are put into the mouth of Llywarch himself, although they were clearly composed somewhat later, possibly in the 9th century. It is possible that these were passed down orally before being transcribed at a much later date. The Canu Heledd, concerning the fall of the kings of the Pengwern region, and the elegy Geraint son of Erbin, concerning the Battle of Llongborth, are also associated indirectly with Llywarch.
Works attributed to him include:
Let the Cock's Comb Be Red
Usual is the Wind
the Calends of Winter
Entangling is the Snare
Bright are the Ash Tops
Sitting High Upon a Hill
I Was Formerly Fair of Limb
The Death of Urien
Maenwyn, When I Was Your Age
Geraint son of Erbin
Marwnad Cynddylan'' - Elgy for Cynddylan