Manwgan ap Selyf was an early 7th century King of Powys, the son of Selyf Sarffgadau.

One theory asserts that when Manwgan ap Selyf came to the throne in 613 he was a young boy, which led to an invasion of Powys

Powys

Powys is a local-government county and preserved county in Wales.-Geography:Powys covers the historic counties of Montgomeryshire and Radnorshire, most of Brecknockshire , and a small part of Denbighshire — an area of 5,179 km², making it the largest county in Wales by land area.It is...

 by Eluadd ap Glast (alias Eiludd Powys), the erstwhile King of Dogfeiling

Dogfeiling

Dogfeiling was a minor sub-kingdom and later a commote in north Wales.It formed part of the eastern border of the Kingdom of Gwynedd in early medieval Wales. The area was named for Dogfael, one of the sons of the first King of Gwynedd, Cunedda. It existed from the year 445 until sometime around the...

. The usurper probably managed to hold the throne for some thirty years or more before he was killed fighting the Northumbrians, possibly at the Battle of Maes Cogwy (Oswestry

Oswestry

Oswestry is a town and civil parish in Shropshire, England, close to the Welsh border. It is at the junction of the A5, A483, and A495 roads....

) in 642. The Dogfeiling dynasty was finally crushed by the Saxons

Saxons

The Saxons were a confederation of Germanic tribes originating on the North German plain. The Saxons earliest known area of settlement is Northern Albingia, an area approximately that of modern Holstein...

around 656, and Manwgan was able to take his rightful place on the Powysian throne.