Ayn Rand is one of America's great mysteries. She was an amphetamine-addicted author of sub-Dan Brown potboilers, who in her spare time wrote lavish torrents of praise for serial killers and the Bernie Madoff-style embezzlers of her day. She opposed democracy on the grounds that "the masses"—her readers—were "lice" and "parasites" who scarcely deserved to live. Yet she remains one of the most popular writers in the United States, still selling 800,000 books a year from beyond the grave. She regularly tops any list of books that Americans say have most influenced them. Since the great crash of 2008, her...