What nickname was sometimes applied to the King who signed a treaty with the men of Kent at the site of Stone Castle ?
Stone Castle:  It was built between 1135 and 1140 on the site where William the Conqueror signed a treaty with the men of Kent in 1067. William the Conqueror: William I (c. 1028 – 9 September 1087), usually known as William the Conqueror and sometimes William the Bastard, was the first Norman King of England, reigning from 1066 until his death in 1087.
William the Bastard