William I, Count of Boulogne

[1] In 1153, Stephen agreed to pass over William's elder brother Eustace IV of Boulogne as heir to the throne, conceding the succession to Henry Plantagenet, son of his cousin and rival Empress Matilda.

Eustace died shortly afterwards and when his father signed the Treaty of Wallingford, William received the lands intended for both brothers, making him immensely rich.

The treaty ended the Anarchy, a succession struggle between Stephen and Matilda of which both sides were growing weary.

Stephen died in 1154, and Henry initially allowed William to retain the earldom of Surrey jure uxoris (in right of his wife).

The plan was to assassinate Henry in Canterbury, and allegedly William had knowledge of this plot or was in connivance with the mercenaries.