Warden of the White Knife is a title used by House Manderly of White Harbor. The predecessor of the city of White Harbor, the castle of the Wolf's Den, was raised by King Jon Stark to guard the mouth of the White Knife at the Bite. After being expelled from the Reach, the Manderlys received the Wolf's Den from House Stark in return for loyally defending the river for their new liege lords in Winterfell.
A Dance with Dragons
The current Warden of the White Knife is Lord Wyman Manderly.