(FORTUNE Magazine) – IKEA founder Ingvar Kamprad insists on flying coach, takes the subway to work, drives a ten-year-old Volvo, and avoids suits of any kind. It has long been rumored in Sweden that when his self-discipline fails and he drinks an overpriced Coke out of a hotel minibar, he will go to a grocery store to buy a replacement. It's clear that this is a frugal man. But is he the richest man in the world? That's a matter of some debate.

Kamprad made headlines in early April, when the leading Swedish business weekly, Veckans Affarer, reported that he was worth $52.5 billion, which would top Bill Gates' $46.6 billion. IKEA quickly denied the claim. So did Forbes, which places Kamprad at No. 13 on its rich list. (Kamprad declined to comment for this article. In fact, he rarely talks to the press. On one of the few times he has spoken to FORTUNE, in 1989, he tried to defend himself against charges of cheapness: "I seldom wash disposable plastic glasses anymore.")

The saga of the Bill Gates of Sweden began in 1943, when Kamprad founded IKEA at just 17 years old. Back then it was a catalog company that sold pens, picture frames, wallets, and other bargain goods. The name IKEA comes from Kamprad's initials and his hometown (the farm Elmtaryd outside the village of Agunnaryd). A small-town guy, Kamprad used his village's milk van to deliver his products when he first started his business. In 1951, IKEA began selling furniture made by local carpenters; six years later Kamprad opened the first IKEA store in Sweden. In 1985 the first U.S. IKEA--which measured three football fields long--opened in a Philadelphia suburb called Plymouth Meeting. Today IKEA is the largest furniture store in the world, with sales of $12.2 billion. Though Kamprad stepped down as CEO in 1999 to comply with Dutch age retirement laws for chief executives, he's still very active in running the company and often suggests furniture ideas, the company says.

There is no question that Kamprad, whose official home is in Switzerland (lower taxes), is among the world's richest men, but his net worth is a bit of a mystery because of IKEA's byzantine ownership structure. The 78-year-old entrepreneur claims to have been preparing for his death for more than 20 years, and in 1982 he established an intricate system of foundations, trusts, and holding companies to avoid high taxes and ensure that IKEA could not be broken up by family infighting. Kamprad has three sons, who all work for the company (he likes to say that IKEA is his fourth child).

The setup makes sifting through his personal finances nearly impossible. The company stores are officially owned by the Dutch foundation Stichting INGKA; other entities own other chunks of the business. After sorting through company documents, Bo Pettersson, the Veckans magazine writer who has long covered all the richest families in Sweden, determined that Forbes had been underestimating both the value of privately held IKEA and the royalties Kamprad gets from the web of entities that together own the company. According to Pettersson's math, IKEA, which makes up most of Kamprad's wealth, was valued at more than $50 billion last year. Also adding to Kamprad's wealth, Pettersson argues, is the continued strength of the Swedish krona against the dollar.

"IKEA is incredibly profitable with margins in the double digits and growing," says Stellan Bjork, author of a Swedish book that provided the first detailed look at the company's complicated financial structure. Bjork thinks the $53 billion figure is too high but says, "American estimates I believe are too low." There's one thing, however, that everyone can agree on: Kamprad's burn rate sure is slower than Gates'.

--Cora Daniels, with additional reporting by Adam Edstrom