House Locke of Oldcastle is an ancient northern house of First Men descent, whose lords once ruled as kings in their own right in the long years after the Long Night. Like so many of the old northern lines they were in time reduced to vassals by the Kings of Winter of House Stark, and they have kept faith with Winterfell ever since. For a span they held the Wolf's Den upon the White Knife: after House Greystark was extinguished the Flints garrisoned that grim old castle for a century, and the Lockes for the better part of two centuries more. Their arms are two bronze keys crossed upon a white pale on a field of purple, and no words of theirs are set down in the histories. Twice the blood of the house has mingled with the Starks', for Lady Lysa Locke wed Lord Benjen Stark and bore him Rickon and Bennard, and Lady Marna Locke wed Lord Edwyle Stark and was mother to Lord Rickard.
At the opening of A Game of Thrones the house is held by Lord Ondrew Locke, an old man who begs off the harvest feast at Winterfell, too frail to dare the journey. His kin fare hard in the wars that follow. Ser Donnel Locke is taken by the Lannisters, presumably at the battle on the Green Fork, and held at Harrenhal until Roose Bolton frees him; riding afterward to Lord Edmure Tully's wedding at the Twins, the Lockes are caught on the wrong side of the Trident and suffer heavy losses when Ser Gregor Clegane falls upon them at the fords, and in the slaughter of the Red Wedding Catelyn Stark sees Donnel cut down by crossbow bolts. Ser Mallador Locke marches with Jeor Mormont's great ranging, charged with the baggage train and the packhorses, and is not among those who straggle back to Castle Black after the disaster at the Fist of the First Men and the mutiny at Craster's Keep. A daughter of the house, Lady Sybelle Locke, wed to Robett Glover, is held captive with her children at Deepwood Motte by Asha Greyjoy.
By the close of A Dance with Dragons the overlordship of the north has passed from the fallen Starks to House Bolton, and Oldcastle answers, in seeming at least, to the Dreadfort. Yet the loyalty of the Lockes is a grudging thing: an unnamed Locke speaks against Ramsay at Lord Wyman Manderly's Merman's Court in White Harbor, and though Lord Ondrew's crossed keys are seen among the banners at Barrow Hall and follow Roose Bolton to Winterfell for Ramsay's wedding, Lord Wyman reckons that the Lockes of Oldcastle will take their lead from White Harbor and not from the Dreadfort.