Deheubarth (literally, "south part") was a south-western petty kingdom or principality of medieval Wales.

Deheubarth was founded circa 920 by Hywel Dda ("Hywel the Good") out of the territories of Seisyllwg and Dyfed, both of which had come into his possession. Later on, the Kingdom of Brycheiniog would also be added to its territory. The chief seat of the rulers of Deheubarth and its traditional capital was at Dinefwr (although Carmarthen and Cardigan also served as the kingdom's capital for certain periods).

Deheubarth, like several other Welsh Petty kingdoms, continued to exist until the Norman Conquest of Wales, but constant power struggles meant that only for part of the time was it a separate entity with an independent ruler. It was annexed by Llywelyn ap Seisyll of Gwynedd in 1018, then by Rhydderch ab Iestyn of Morgannwg in 1023. Llywelyn ap Sisyll's son, Gruffydd ap Llywelyn again annexed Deheubarth and became ruler of most of Wales, but after his death the old Dinefwr dynasty regained power.

Gerald of Wales (c. 1146 – c. 1223), also known as Gerallt Gymro in Welsh or Giraldus Cambrensis in Latin, archdeacon of Brecon, was a medieval clergyman and chronicler of his times. Born ca. 1146 at Manorbier Castle in Pembrokeshire, Wales, he was of mixed Norman and Welsh descent; he is also known as Gerald de Barri.

Gerald was son of William FitzOdo de Barry (or Barri), the common ancestor of the Barry family in Ireland and one of the most powerful Anglo-Norman barons in Wales at that time. He was a maternal nephew of David fitzGerald, the Bishop of St David's and a grandson of Gerald de Windsor (alias FitzWalter), Constable of Pembroke Castle, and Nest the daughter of Rhys ap Tewdwr. Through their mother, Angharad, Gerald and his siblings were closely related to Angharad's first cousin, Rhys ap Gruffydd, the Lord Rhys (Yr Arglwydd Rhys), and his family.