Cadafael, King of Gwynedd

He came to the throne when his predecessor, King Cadwallon ap Cadfan, was killed in battle, and his primary notability is in having gained the disrespectful sobriquet Cadafael Cadomedd (fully translated into English: Battle-Seizer the Battle-Decliner).

There was an alliance of the Cymry with Penda of Mercia initially forged by Cadwallon ap Cadfan, and there was ongoing warfare against the then-ascendant Kingdom of Northumbria.

Though the alliance was effective and enjoyed several notable successes, it would end disastrously with the death of Penda and a Northumbrian supremacy both in the north and in the English Midlands.

Together they would contest Northumbria's rise, and the alliance would ultimately defeat and kill Edwin in 633 at the Battle of Hatfield Chase (Welsh: Gwaith Meigen) near Doncaster in South Yorkshire.

Eanfrith's Bernician successor Oswald would reunite Northumbria into one kingdom, leading off at the Battle of Heavenfield (Bellum Cantscaul in the Annales Cambriae) near Hexham in 634, where he defeated and killed Cadwallon.

Northumbria secured the entire eastern coastal region of Lothian (i.e., Gododdin) in 638 or shortly thereafter, and there were battles against the men of Alt Clud (the Brythonic predecessor state of Strathclyde) in the 640s.

[4] The defining moment came in 655 when Penda again led an alliance of Mercians, Welsh, Deirans, and East Anglians against Bernicia,[5] besieging Oswiu at a stronghold somewhere in the north and compelling him to sue for peace.

With many of its leaders having been killed in battle, the alliance was caught unawares in a sortie by Oswiu at the Winwaed (Welsh: Maes Gai, its location uncertain).

Oswiu would go on to re-unite Bernicia and Deira into Northumbria and establish a temporary dominance over Mercia, becoming the premier military and political power north of the Humber Estuary.

There is no contemporary account of the events, but writing some 180 years later Nennius would say that Cadafael had left for home the night before the battle, in his ally's hour of greatest need, implying it was a deliberate decision (i.e., by calling him the Battle-Decliner).