Aethelbald was a King of the west Saxon kingdom of Mercia. It is not known for certain when he was born, but we do know that by 731 he had established himself as bretwalda, or overlord, of all the territory south of the River Humber. Around 743 he joined forces with Ceolred of Wessex to invade Powys and Gwent.
In 749 Aethelbald called a special Synod, or church summit, at Gumley, at which he agreed to keep monasteries exempt from Royal service. In 752 he lost the Battle of Burford to Cuthred of Wessex and thus lost his claim to overlordship of Mercia.
Though his reign was [unusually for that time period] a time of somewhat relative peace, the end was not; he was murdered by his bodyguard in the year 757, paving the way for Beornred to claim the kingship. Beornred was quickly overthrown by Aethelbald's cousin Offa, probably the greatest of all the Mercian kings.