In Welsh-Deiniol, in Latin-Dainiolus and in English-Daniel.
Deiniol, born in the early 6th century, was an important figure in the development of Christianity in North Wales. The son of a Celtic chieftain, he founded two monasteries, both named Bangor, one of which was close to the modern town of that name…
These were flourishing houses, allegedly with a total of over 2000 monks; many were to perish near Chester at the hands of a pagan king of Northumbria. Deiniol himself is regarded as the first bishop of Bangor. There are numerous dedications to him in North Wales (including the famous library which the Prime Minister Gladstone established in his country seat at Hawarden, near Chester), but few in the South.
In 545 he and St. Dyfrig, who worked in the border country, took part in a synod with St. David which settled many matters regarding the discipline of penance (something over which Celtic Christians enthused); this suggests that Deiniol was regarded as David’s equal. He died in about 584.
From Here