Coenwulf became king in 796 after the death of Ecgfrith. Ecgfrith, the son of Offa, ruled for only five months and there is speculation that Coenwulf was responsible for Ecgfrith's death. Coenwulf's claim to the throne was his descent from Cenwalh, who was a younger brother of past kings that had ruled Mercia 150 years prior to Coenwulf's ascension to the throne. In 796, Kent rebelled against Mercia, which had ruled Kent since 785. Coenwulf won the support of the church largely due to the Church's dislike of Aethelheard, Archbishop of Canterbury, who had fled the country at the beginning of the rebellion. By 798 Coenwulf had successfully invaded Kent and captured the rebellious king Eadbert Praen. Coenwulf named his brother Cuthred the king of Kent after Praen's capture. Cuthred ruled until his death in 807, after which Coenwulf took control of the country himself.
Throughout his reign, Coenwulf successfully waged wars against East Anglia and the Welsh of Powys and Gwynedd. Coenwulf's reign was filled with turmoil and blood shed, mostly that of the opposition. Mercia continued to hold military supremacy in the region until the 820s, after Coenwulf's death. Mercia did experience some rebellion and opposition, but under Coenwulf there was either a peaceful resolution to any conflicts or Coenwulf made certain that Mercia was victorious in the event a resolution could not be reached. Coenwulf reigned until his death in 821. Coenwulf's brother Ceolwulf I succeeded him as king of Mercia immediately after his death.
There is one gold coin in existence that bears the name of Coenwulf. A 1200-year-old gold penny was discovered in England alongside the River Ivel. This coin was sold to an American collector for 230,000 pounds at an auction.
image courtesy of Spink