Sir William Stanley (c. 1435-1495), brother of Thomas Stanley, first Earl of Derby, whose intervention at Bosworth decided the battle.

The consequences of that intervention were long remembered on both sides. The death of the Duke of Norfolk in the battle was imputed to Sir William Stanley, and a feud ran between the Howards and the Stanleys from Bosworth onward, so that the Howards were slow to admit how much they owed the Stanleys for the later victory at Flodden. A Lord Derby put it plainly enough: my uncle slew his father dear, he would have avenged him on me. Sir William's own end came ten years after Bosworth, when he was executed for treason, and John Ford afterwards made his fate part of the play of Perkin Warbeck.

A different and earlier Sir William Stanley matters more to the Island. Sir John Stanley the first, who was the first King or Lord of Man under the grant of Henry IV, was the second son of a Sir William Stanley. That Sir John was knighted by Edward III, made Governor or Lieutenant of Ireland by Richard II about 1379, held the office until 1389, was appointed Lord Justice of Ireland in 1390, and appears never to have visited the Island at all.