King Offa was King of Mercia, and was a mentioned character in Season 2 and the father of Kwenthrith of Mercia.
Biography
History
After the King offa's death, Kenelm took the Mercian throne. Unfortunately, the young King died shortly thereafter and rumors soon started that he was killed by his sister, setting off a nasty civil war as Kwenthrith becomes one of the leading claimants of the Mercian crown.