Alba
The ruler of Alba was King Malcolm II (Malcolm the Destroyer), who had ruled since 1005 and would continue to do so until 1034.
Deheubarth
King Edwin ab Einion ab Owain ruled jointly with his brother, King Cadell ab Einion ab Owain .
England
The ruler of England was King Cnut (Cnut the Great), who had ruled since 1016 and would continue to do so until 1035.
Gwynedd
The ruler of Gwynedd at the beginning of 1018 was King Aeddan ap Blegywryd, who had ruled since 1005. This year, King Llywelyn ap Seisyll would take over.
Moray
The ruler of Moray was Mormaer Findláech mac Ruaidrí (probably, the start of his reign is shrouded in mystery).
Strathclyde
King Owain Foel but at some point around this time King Malcolm took over.