Æthelred, Lord of the Mercians (or Ealdorman Æthelred of Mercia; died 911) became ruler of English Mercia shortly after the death of its last king, Ceolwulf II in 879. His rule was confined to the western half, as eastern Mercia was then part of the Viking-ruled Danelaw. Æthelred's ancestry is unknown. He was probably the leader of an unsuccessful Mercian invasion of Wales in 881, and soon afterwards he acknowledged the lordship of King Alfred the Great of Wessex. This alliance was cemented by the marriage of Æthelred to Alfred's daughter Æthelflæd.