You'd be hard pushed to find someone who hadn't heard of Gap. Even the most fashion-phobic or apathetic of shoppers has been into one of their 3000-plus stores worldwide. In fact, the most apathetic are probably best acquainted with the brand, because it makes the whole process of shopping so easy. From a single outlet in San Francisco, the chain became a household name by stocking basic and reliable separates that people would always want and need.

Its early success lay in offering people an easy format at a time before the high street had really evolved; the idea of everything in one store was appealing to a fledgling mass market and the wholesome Americana look that Gap purveyed – from preppy to plaid to Pollyanna – struck a chord with buttoned-up traditionalists and laid-back hippies alike.

And the quality was good – consumers back then didn't expect to shell out £2 for a coat that they could throw away like a paper plate, but they recognised fair prices, and they got their money's worth. It's a philosophy that is still with the brand now, and it's one that has paid off, seeing the company through the rise and fall of "fast fashion". Gap remains a favourite both with shoppers stocking up on cheap essentials and with those who want an investment piece that will last several years.

Although not originally known for being at the cutting edge of trends, Gap has in recent years concentrated on seasonal collections that are more design-led (without scaring off its traditional fanbase, of course), with simple but refined chic pieces a world away from its casualwear roots.

It also developed a new kind of high-street shopping with the first designer collaboration, a range of shirt dresses in 2006 by Roland Mouret, which has been followed up by capsules from established designers, such as Pierre Hardy, and new designers Thakoon and Alexander Wang. It's a supremely clever way of encouraging the young and fashion-conscious into a shop they may not otherwise frequent. And funding young talent means Gap has a hotline to editors and industry leaders alike.

The sad news of Donald Fisher's death coincides with the brand's 40th anniversary, and there's a sense that Gap has really come of age. It's not fair to call it the clothing equivalent of McDonald's, but its blue and white livery is as much a part of our cultural fabric as the golden arches.