April 25 (Reuters) - Walmart said on Thursday that Rob Walton would retire from the board of the big-box retailer at the end of his term on June 5.

Walton, the eldest son of Walmart founder Sam Walton, served as the company's chairman of the board of directors from 1992 to 2015, according to a bio on the company's website.

After joining the company in 1969, Walton held several roles, including senior vice president, corporate secretary, general counsel and vice chairman.

"His leadership has been critical as we've grown our business over so many years," Greg Penner, the current Chairman of Walmart's board said in a regulatory filing announcing Walton's retirement.

The Walton family is the richest family in America, according to Forbes, thanks to their stake in the retailer, the world's largest by sales. (Reporting by Granth Vanaik in Bengaluru; Editing by Shilpi Majumdar and Bill Berkrot)