The ruler of England at the beginning of 1100 was King William II (William Rufus), who had ruled since 1087. This year, King Henry I (Henry Beauclerc) would take over.
The ruler of Gwynedd was King Gruffydd ap Cynan, who had ruled since 1081 and would continue to do so until 1137.
The ruler of Moray at this time was likely to have been Mormaer Oenghus mac inghine Lulaich.
The ruler of Scotland was King Eadgar (The Valiant), who had ruled since 1097 and would continue to do so until 1107.