Tadashi Yanai, Japan's richest man, used advice from management guru Peter Drucker to build his Uniqlo clothing empire. To pull out of a slump that's hammered profits and shares, the billionaire is revisiting the lessons.

Yanai, 61, founder and president of Fast Retailing Co., built his estimated $9.2 billion fortune over 26 years, turning his father's tailor shops into the Uniqlo chain of low-priced casual wear to become Asia's biggest clothing retailer. Yanai says his success was inspired by Drucker's management strategies and the idea of "customer creation" with a product that creates demand.

This year, something went wrong with Yanai's strategy. Fast Retailing's shares have plunged 26 percent in 2010, sales at stores open more than a year fell 25 percent in September, continuing to slide through November, and the company forecast its first profit decline in four years for the fiscal year ending in August.