Æthelred's descent is unknown, and he does not appear to have been closely related to his immediate predecessors, although his name suggests possible descent from earlier Mercian kings. He may have been related to King Alfred's Mercian father-in-law, Æthelred Mucel, and brother-in-law, Æthelwulf, who appears to have been a member of Æthelred's court from the mid 880s. Æthelred may have been the man of the same name who attested two Mercian charters in the late 860s, but he is not listed in the two surviving charters of Ceolwulf. Lists of witnesses to charters show that Æthelred's witan (council) shared bishops and at least two ealdormen with Ceolwulf, but Ceolwulf's thegns all disappeared. In the view of Ian Walker: "He was a royal ealdorman whose power base lay in the south-west of Mercia in the former kingdom of the Hwicce around Gloucester." However, Alex Woolf suggests that he was probably the son of King Burgred of Mercia and Æthelswith, sister of Alfred the Great, although that would mean that Æthelred's marriage was uncanonical, as Rome then forbade marriage between first cousins.