TOKYO, Feb 19 (Reuters) - Strong sales at recession-proof discount clothing retailer Uniqlo have made company founder Tadashi Yanai Japan's richest man, worth $6.1 billion, Forbes magazine said in its annual rankings.

The net worth of the 60-year-old Yanai jumped $1.4 billion in the past year, bumping him from sixth place to surpass Hiroshi Yamauchi, former chairman of video game maker Nintendo and Japan's wealthiest person last year.

Shares of Fast Retailing (9983.T), which operates a network of more than 800 Uniqlo stores mostly in Japan, surged 63 percent in 2008, bucking a slide in the Japanese stock market and boosting the value of Yanai's 26.7 percent stake.

Uniqlo has emerged as one of the few retailers able to thrive as the world's second-largest economy falls deeper into recession, attracting cost-conscious customers with its cheap but novel offerings of basic apparel.

Yanai was one of only four from last year's top 40 list to see their net worth increase, Forbes said.

The other three were Masahiro Miki, the founder of discount shoe store chain ABC Mart Inc (2670.T), the Kinoshita brothers of consumer lender Acom Co (8572.T) and Chizuko and Michio Matsui of online broker Matsui Securities Co (8628.T).

Yamauchi's wealth dropped by $3.3 billion to $4.5 billion and he slipped to third in the ranking, reflecting a slide in Nintendo's stock price. Property tycoon Akira Mori is $3.5 billion poorer, slipping two notches to the No. 4 spot.

Uniqlo has often been called the Gap Inc (GPS.N) of Japan.

Fast Retailing still trails far behind the U.S. retailing giant in terms of total revenues but Yanai is now richer than Gap founder Donald Fisher and family, which have a net worth of $5.1 billion, according to Forbes. (Reporting by Nathan Layne; Editing by Chris Gallagher)