In 1986, Sam Walton, the founder of Wal-Mart, had a problem. He was under growing pressure from shareholders — and his wife, Helen — to appoint a woman to the company’s 15-member board of directors.

So Mr. Walton turned to a young lawyer who just happened to be married to the governor of Arkansas, where Wal-Mart is based: Hillary Rodham Clinton.

Mrs. Clinton’s six-year tenure as a director of Wal-Mart, the nation’s largest company, remains a little known chapter in her closely scrutinized career. And it is little known for a reason. Mrs. Clinton rarely, if ever, discusses it, leaving her board membership out of her speeches and off her campaign Web site.

Fellow board members and company executives, who have not spoken publicly about her role at Wal-Mart, say Mrs. Clinton used her position to champion personal causes, like the need for more women in management and a comprehensive environmental program, despite being Wal-Mart’s only female director, the youngest and arguably the least experienced in business. On other topics, like Wal-Mart’s vehement anti-unionism, for example, she was largely silent, they said.