Penda of Mercia
Around 606 AD, Pybba King of Mercia died leaving behind a young family. His infant son, Penda, grew up in the shadow of his father's reign, and would eventually rule over Western Mercia and the territory of Hwicce. Yet Penda was blood-thirsty, and it was widely-known that his territories were hostile, aggressive and tribal. Penda's wish to rule over more territories sparked a lifetime of bloody battles, proving that he was both an exceptional ruler, and an outstanding warrior.
In 626, when he was around twenty-five years old, Penda became the King of Mercia. The Anglo-Saxon Chronicle writes that shortly after Penda's accession to the Mercian throne, he fought with Cynglis King of Wessex, and his heir, Cwichelm. They fought "at Cirencester and came to an agreement [...] there" (Thorpe, 1861). Historians believe that within the terms of this agreement, the county of Cirencester was to be handed to Penda in return for a marriage alliance to Cynglis' sister, Cynewise.
Later, in 633, Penda united with Cadwallon ap Cadfan, the King of Gwynedd, to invade Northumbria, a kingdom that Penda would be notoriously hostile to until his death. This hostility culiminated with The Battle of Hatfield Chase, that occurred in 633, and ended with the death and defeat of Edwin, King of Northumbria. Penda and Cadwallon destroyed the land before returning to their respective kingdoms. Penda had captured Eadfrith, the son of Edwin, and kept him as hostage, but just years later Eadfrith was murdered on Penda's orders (Ashley, 1999). It was not the last time Penda would fight the Northumbrians - in 634, King Oswald of Northumbria met Penda at Oswestry, where Penda avenged his ally Cadwallon, who had been killed by Oswald. Penda was yet again victorious, and it was clear that he was perhaps one of the strongest militant leaders and most-capable fighters of his time.
And it didn't stop there. Penda would go on to kill two more Anglian kings - Egric and Sigebert, defeating them in battle and claiming their territories in the East. Historians believe that it was around this time that Penda appointed his younger brother Eowa as a secondary king of Mercia, intending him to rule the North whilst Penda ruled the lands that he had claimed in battle.
More difficulties arose in 645, when Penda's peace treaty with the kingdom of Wessex was broken. When the new King of Wessex, Cenwalh, refused to marry Penda's sister, Penda grew outraged and attacked Wessex. Along with his son Wulfhere, Penda was successful in pushing back the Wessexians and claimed their territories. When Cenwalh fled to East Anglia, Penda followed him, slaying King Anna of East Anglia as a lesson to those who protected traitors. Penda had yet again been victorious, and he quickly began to gain a reputation as an undefeated king.
But his success would not last forever. In 654 Penda marched out to meet King Oswiu of Northumbria at the Battle of the Winwaed, but despite his vast army and impeccable success rate, Penda was struck down. He died on the 15th November 655 in Leeds, aged around fifty years old.
According to the Anglo-Saxon Chronicle, Penda reigned for "thirty winters" (Thorpe, 1861). He was succeeded by his eldest son Peada, who became the King of Mercia. His sons Wulfhere and Aethelred would in time also become Kings of Mercia, whilst his daughter Wilburh became Queen of Surrey. Two of Penda's children, Eadgyth and Eadburh, also became saints. Although Penda was a Pagan, and therefore probably poly-amorous, he was by all accounts faithful to his wife Cynewise, who was a well-respected and well-liked woman. Penda's death marked the end of Pagan kingship in England (Historic UK).
Sources
Ashley, M., The Mammoth Book of British Kings and Queens (New York: 1999).
Blair, P. H., Roman Britain and Early England - 55 B.C. - A.D. 871 (New York, 1966).
Historic UK, Kings and Queens of Mercia, 515 - 918 AD (https://www.historic-uk.com/HistoryUK/HistoryofEngland/Kings-Queens-of-Mercia/).
Thorpe, B., The Anglo-Saxon Chronicle: Translation (London, 1861).