The Wikipaedia summary of Penda is as follows:
Penda (died November 15, 655) was a 7th-century King of Mercia, a kingdom in what is today the English Midlands. A pagan at a time when Christianity was taking hold in many of the Anglo-Saxon kingdoms, Penda participated in the defeat of the powerful Northumbrian king Edwin at the battle of Hatfield Chase in 633.
Nine years later, he defeated and killed Edwin's eventual successor, Oswald, at the battle of Maserfield; from this point he was probably the most powerful of the Anglo-Saxon rulers of the time. He defeated the East Angles, drove the king of Wessex into exile for three years, and continued to wage war against the Bernicians of Northumbria. Thirteen years after Maserfield, he suffered a crushing defeat and was killed at the battle of the Winwaed in the course of a final campaign against the Bernicians.