Alba
The ruler of Alba was King Kenneth III (Kenneth the Brown), who had ruled since 997 and would continue to do so until 1005.
Deheubarth
The ruler of Deheubarth at the beginning of 999 was King Maredudd ab Owain ap Hywel, who had ruled since 986. This year, King Cynan ap Hywel ap Ieuaf would take over.
England
The ruler of England was King Æthelræd II (Æthelred the Unready), who had ruled since 978 and would continue to do so until 1013.
Strathclyde
The ruler of Strathclyde at this time was likely to have been King Owain Foel.