William, Earl of Glenallan, otherwise Lord Glenallan, is a character in Sir Walter Scott's 1816 novel The Antiquary, a Scottish aristocrat whose life has been ruined by the suicide of his wife and the belief that he has unwittingly committed incest. His story forms the melodramatic Gothic strand in an otherwise largely realistic comic novel.

The Antiquary (1816), the third of the Waverley novels by Walter Scott, centres on the character of an antiquary: an amateur historian, archaeologist and collector of items of dubious antiquity. He is the eponymous character and for all practical purposes the hero, though the characters of Lovel and Isabella Wardour provide the conventional love interest. The Antiquary was Scott's own favourite of his novels, and is one of his most critically well-regarded works; H. J. C. Grierson, for example, wrote that "Not many, apart from Shakespeare, could write scenes in which truth and poetry, realism and romance, are more wonderfully presented."