Leonard Riggio, a brash, self-styled underdog who transformed the publishing industry by building Barnes & Noble into the country’s most powerful bookseller before his company was overtaken by the rise of Amazon.com, has died at age 83. Riggio died Tuesday “following a valiant battle with Alzheimer’s disease,” according to a statement issued by his family. Riggio’s near-half century reign at Barnes & Noble began in 1971 when he used a $1.2 million loan to purchase the company’s name and its flagship store on lower Fifth Avenue in Manhattan.