Offa, king of the Mercians (757 – 96), son of Thingfrith the son of Eanwulf, was first cousin to Æthelbald 4, king of the Mercians (716 – 757). Offa 7 became king of the Mercians after driving out Æthelbald 4’s short-lived successor, Beornred 1. By the end of his reign Offa 7 was the most powerful king in England and, to varying extents, exercised lordship over Sussex, Kent, Essex and East Anglia, although it is unlikely that he exercised any direct lordship over Wessex or Northumbria. His reign has come to be viewed as a period of significant military and urban development in the face of Viking depredations.
S. Kelly, ODNB; BEASE, 340 – 1; F. M. Stenton, ‘The supremacy of the Mercian kings’, Preparatory to ‘Anglo-Saxon England’: being the collected papers of Frank Merry Stenton, ed. D. M. Stenton (1970), 48–66; P. Wormald, 'The Age of Offa and Alcuin', in The Anglo-Saxons ed. J. Campbell (1982), pp 101 – 28; J. Haslam, ‘Market and fortress in England in the reign of Offa’, World Archaeology 19 (1987), 76 – 93; D. Hill & M. Worthington (ed.), Æthelbald and Offa: two eighth-century kings of Mercia.