Even for those who know everything there is to know about fashion, the name Amancio Ortega rings few bells. The fact that he is currently at number 25 on the Forbes billionaire list, with a $9.1bn fortune, has done nothing to increase his renown. That he is the richest man in Spain - and, after Bernard Arnault, head of luxury goods conglomerate LVMH (Louis Vuitton Moët Hennessy), the richest man in fashion - has not made the slightest dent in our collective interest.

This is, of course, exactly how the 65-year-old textile billionaire wants it to be. He's happy running his soaringly successful business from the Galician port of La Coruna, away from the political gossipmongering of Madrid and the style obsessions of Barcelona. But if he isn't the subject of discussion, his company is.

Ortega is the founder and president of Inditex, the parent company for which Zara, the high-fashion chain currently rampaging down Britain's high streets, makes 78% of the profit. He has never given a media interview and only two photographs of him are available, identical but for the fact that he is smiling in one and scowling in the other.

Many in the industry couldn't tell you where Zara has its headquarters (Arteixo-La Coruna is hardly fashion central, after all), though everyone knows the brand. There are no press offices outside Spain, and even the communications department in Arteixo does anything but. The company doesn't lend clothing samples for editorial fashion shoots. It does no advertising (marketing accounts for 0.4% of Zara's total spend).

What it has done is plug a gap in the market with a desirable product: high-fashion clothing for middle-class urban women. Detractors say that Zara simply rips off designers ("We spend a fortune researching and working up ideas, then Zara comes along and walks off with them for nothing," says one). But Jose Antonio Guerrero, a consultant who has worked for the company, says: "Zara doesn't copy too obviously. The results would be too rough if they did. But they do adapt and carry through principal ideas, yes."

Yesterday, Zara HQ revealed that it had secured its first premises in Russia - the 44th country to get a taste of its cut-price chic. Two weeks ago, Zara's largest European store - a 3,000 sq m temple to consumption - opened on the corner of Oxford Street and Bond Street, its location rather conveniently summing up Zara's knack for offering high-style clothes at high-street prices. In typical Ortega fashion, until it opened on Friday morning, the building was completely concealed beneath hoardings with no indication of who was about to launch themselves into the Oxford Street melee. Rumours abounded. By the time the store was ready, the Zara faithful had spread the word.

Within minutes of the doors opening, the tills were ringing and shoppers leaving laden with the easily identifiable navy paper bags. Among the bewildering selection of clothes, I spotted a passable interpretation of a Christian Dior embroidered Afghan on the rails (£95), a Pradaesque brocade waistcoat (£45) and a black wool coat (£65) that was enticingly similar to something by superchic Italian label Costume National (£565). An assistant even pointed me in the direction of what he called "the Anna Sui collection", an up-to-the-minute assortment of patchwork, denim and boho chic. (Sui is a veteran New York designer who shows on the catwalk.)

The speed at which Zara translates catwalk styles into high-street products is the key to its success. It can do this because it controls manufacturing more closely than any of its competitors - Gap, for example, or H&M - by producing 50% of its product in-house. Another 46% is farmed out in ready-cut pieces to workshops around the Iberian peninsula. "It's both supplier and retailer," says Richard Hyman, chairman of retail analyst Verdict. "And that makes it incredibly fleet of foot."

If a style doesn't sell well within a week, it is withdrawn from shops, further orders are cancelled and a new design is pursued. No model stays on the shop floor for more than four weeks, which encourages Zara zealots to make repeat visits. An average high-street store in Spain expects fans to visit three times a year. That goes up to 17 times for Zara. "The girls in the office know that new stock comes in on Tuesday and Thursday, and off they go," says Julian Vogel, joint managing director of fashion PR company Modus. "It's a guilt-free high."

The high street holds no shame for the fashionista these days. Especially not when the product is this good. Current fashion favourite Matthew Williamson proudly announced he was dressed in H&M menswear during the latest fashion week; Dani Behr wears Zara on TV; supersophisticate designer Roland Mouret has seen his slinky tops reproduced by Morgan; and everyone under 30 knows Top Shop is the key to ultimate fashion fulfilment.

Susie Forbes, deputy editor of British Vogue, says: "My everyday Vogue life is spent in Zara: Zara jeans, a Marc Jacobs-type chiffon shirt and velvet paisley jacket. Seventy per cent of my wardrobe is from the store. My £70 pea coat is in its second year."

Such adoration from the picky fashion set must be a source of at least a little astonishment for the self-made Ortega, son of a railway employee and a cleaner. He entered the textile industry as a runner for a Corunan shirtmaker. By 1963 he had accrued the handsome sum of 5,000 pesetas - £18 in today's money - and used it to set up his own small company making pyjamas and dressing gowns. In 1975, as he turned 40, he opened the first local Zara store.

The brand spread slowly through Spain, and Ortega's ambition didn't become evident until 1989, when he opened first a store outside Spain (Oporto, Portugal), then outside the Iberian peninsula (Paris), then outside Europe (New York). The company didn't reach London until 1998, but the name had. Susie Forbes says she queued outside the Regent Street store on its opening day.

Ortega achieved megabucks status in May 2001 when the company launched itself on the Madrid Stock Exchange. Morgan Stanley, in charge of the IPO, refers to its "peerless track record". Ortega, who had retained a 61% interest in the business - then showing profits of around $240m - saw shares increase from their initial value of 14.7 by 22%. He was a billionaire, and celebrated by buying a Falcon 900 executive jet and a stake in Spanish football club Deportivo la Coruna. Not quite the same as splashing out £50 on a new Zara top for the weekend, but strangely enough, part of the same continuum.

We gave two people £100 each to buy a whole outfit from Zara: here is what they came back with. And Guardian fashion writer Laura Barton offers her verdict

His

The distinctly kaftan-esque top (£25), with its deep-cut neckline, gives a nod to Roberto Cavalli, the man we have to thank for David Beckham's splendid look at David Furnish's birthday party only last week. The sleeveless T-shirt (£9), meanwhile, will keep the cold off your chest. Cord is still big news this season, and these needle cord trousers (£35) are a dead ringer for those seen at the Dolce and Gabbana show. Long scarves are this winter's essential accessory, and Zara's version (£18) comes in nice manly, sludgey colours.

Total: £87

HersThis wrap-over top (£25) is a nice example of an item which can go horribly wrong. Zara's version is in a heavy fabric which will hang well and looks a bit classier than most high-street versions. Cropped trousers have been everywhere this season, notably in the Nicole Farhi and Paula Ka collections. Zara's pair (£49) are nicely baggy, will look grand with a pair of knee-high boots, and avoid looking like the dreaded culottes. Belts have been the hot accessory for a while now, and as we march towards 2003 the trend proves unrelenting. Zara's broad leather version (£9) will finish off this outfit perfectly.

Total: £83