Who is St. David?

regarded as the heavenly advocate of a nation) saint Wales.
David is believed to have been born near the present day city that bears his name, in Pembrokeshire, South West Wales. The exact year of his birth is unknown, with estimates ranging from 462 to 515 AD.
Much of what we know about David comes from Rhygyfarch, the 11th century author who wrote the Life of Saint David. As it was written so long after the fact, its reliability is questionable. 

Capel Non's, to the south of the city that bears his name. It is thought that Non was a victim of violation by Sandde after she resisted his initial advances. Non became a nun and was later canonised.

said to have been baptised at nearby Porthclais by St Elvis of Munster. It is said that a blind monk, Movi, was cured after drops of water splashed into his eyes as he held David.

a popular poem which prophesied that in the future, when all might seem lost, the Welsh people would unite behind the standard of David to defeat the English; "A lluman glân Dewi a ddyrchafant" ("And they will raise the pure banner of Dewi").

composer Karl Jenkins"Dewi Sant". It is a seven-movement work best known for the classical crossover series Adiemus, which intersperses movements reflecting the themes of David's last sermon with those drawing from three Psalms. An oratorio by another Welsh composer Arwel Hughes, also entitled Dewi Sant, was composed in 1950.