Æthelred, Lord of the Mercians (or Ealdorman Æthelred of Mercia) (died 911) becomes ruler of Mercia shortly after the death of its last king, Ceolwulf II in 879.

Æthelred's descent is unknown.

He is probably first recorded as the leader of an unsuccessful Mercian invasion of Wales in 881, and in 883 he makes a grant to Berkeley Abbey with the approval of King Alfred of Wessex, showing that he acknowledged Alfred's lordship.

Æthelred marries Alfred's eldest daughter Æthelflæd between 882 and 887, and they have one child, a daughter called Ælfwynn.After Æthelred's death, Æthelflæd rules as Lady of the Mercians until her own death in 918.