Alba
The ruler of Alba was King Constantine I (Constantine the Wine-Bountiful), who had ruled since 862 and would continue to do so until 877.
Mercia
The ruler of Mercia was King Ceolwulf II, who had ruled since 874 and would continue to do so until 883.
Strathclyde
It is generally thought that the ruler of Strathclyde at the beginning of 876 was King Rhun map Arthgal. About this time King Dyfnwal would take over.
Wessex
The ruler of Wessex was King Ælfræd (Alfred the Great), who had ruled since 871 and would continue to do so until 899.