Cadfan ap Iago (c. 569 – c. 625) was King of Gwynedd (reigned c. 616 – c. 625). Little is known of the history of Gwynedd from this period, and information about Cadfan and his reign is minimal.
The historical person is known only from his appearance in royal genealogies, from his grant to Saint Beuno for the monastery at Clynnog Fawr, and from his inscribed gravestone.
Cadfan was the son and successor of King Iago ap Beli, and is listed in the royal genealogies of the Harleian genealogies and in Jesus College MS. 20. Cadfan came to the throne near the time of the Battle of Chester (Welsh: Gwaith Caerlleon) in 616, in which the Northumbrians under Æthelfrith decisively defeated the neighboring Welsh Kingdom of Powys and then massacred the monks of Bangor Is Coed. However, there is no evidence that Gwynedd had any part in the battle, so Cadfan's accession at that time appears to be no more than coincidence.
Cadfan's gravestone is at Llangadwaladr (English: Cadwaladr's Church) on Anglesey, a short distance from the ancient llys (English: royal court) of the kings of Gwynedd, and reputed to be their royal burial ground. The inscription refers to him as sapientisimus (English: most wise), and as this term is historically used for ecclesiastics, it suggests that at some point, Cadfan had resigned as king to live out his remaining years as an ecclesiast.
Cadfan was succeeded as king by his son, Cadwallon ap Cadfan.