Looking back, there was a time when a luxury brand's identity was defined solely by the designer who founded it.

Stalwarts such as Christian Dior, Cristobal Balenciaga and Yves Saint Laurent were not just leaders of the brands that bore their name, but also visionaries responsible for creating a legacy that would last well after they were gone.

However, as the baton has been passed on to the next generation, many designers have become dispensable, and there has been a series of musical chairs at some of the industry's most powerful brands. Stefano Pilati, Christophe Decarnin, Raf Simons and John Galliano are just a few who have been flung aside from the houses they have defined - or founded - over the past decade.

In their place have come new designers who have been charged with the onerous burden of reigniting the brand, while attempting to juggle the heritage left behind by their predecessors.

The trend favours younger and less experienced names, such as 21-year-old Olivier Rousteing, who is now creative director of Balmain, and New York wunderkind Alexander Wang, who recently debuted his first collection at Balenciaga.

With so many comings and goings, one can't help but wonder how this has affected the identity of each brand. Has a brand's DNA become more fluid, or is it still inextricably linked to the designer at its helm?

"Today, identity can be misinterpreted," explains Jean-Marc Loubier, president and CEO of Fung Brands, who has been responsible for acquiring several luxury brands over the years, including Robert Clergerie, Sonia Rykiel and Delevaux.

"When people say identity they are often referring to the codes or signatures of a house. Sure, codes are important, but without a soul it is nothing. With identity you need to manage it, play with it, feel it, question it, challenge it, make it bigger and smaller. You have to shape it. The designer should be the leader in that."

I ndeed, it goes without saying that in order to survive, a brand needs to create something new and desirable. For an established house, it is also important to balance past and future, while paying respect to its history and heritage.

For the past 30 years, Karl Lagerfeld at Chanel has excelled at this by creating styles that are fresh and directional, while paying tribute to Chanel's signature codes.

Sarah Burton, at Alexander McQueen, is another example of a designer who has managed to inject new life into a brand, while paying respect to the identity created by its founder.

When she took over as creative director in 2010, many critics questioned whether she would be able to recreate Lee McQueen's dark, tailored designs. Instead, she surprised everyone by not only paying respect to his legacy, but also by injecting a new feminine spirit that won over old and new fans.

"The past is only interesting if you can make the future a success. A brand cannot be set on doing things the same way for 50 years. The identity is a connecting thread, but it also needs to move. You need to use the past to go a step further.

"[A designer] must challenge themselves to bring something original but real because being different may not be enough. You always have to be a kind of forerunner and to add something. It's not about bags or ready to wear - it has to be something meaningful," Loubier says.

In the case of Christian Dior, which was helmed by John Galliano for 15 years, the arrival of former Jil Sander designer Raf Simons was a welcome change.

"From time to time, it can be helpful for a brand to have a [revamp] that builds on the brand's DNA, but also enables the designer to create their own interpretation of the brand," says Imran Amed, founder and editor of industry website, The Business of Fashion.

"The recent reinvention of Dior under Raf Simons is a perfect example of this. Simons has carefully studied the house's heritage, including the Bar jacket and other Dior codes, but has modernised these codes while still respecting the Dior heritage. This has been a very big change from the Dior under John Galliano, which was also respectful of the Dior DNA, but had started to become stale after so many years of the same interpretation."

While Simons has been a success with customers and critics, there are cases when changing creative directors too often can create confusion as to what the brand stands for and represents. Because of this, building a brand's DNA is no longer a task the creative director takes on alone. Today, a brand is driven by a team of people behind the scenes, from artistic directors and photographers to merchandisers and marketing experts.

"Everything is important, it's like a puzzle. Customers are important as they are looking for something special. History and heritage are the foundation you need to build on," says creative consultant Marc Ascoli, who has worked with brands including Jil Sander, Sergio Rossi, Yohji Yamamoto and Chloé.

"Then you also need a strong personality leading the house who can interpret the history with some fantasy, but not in a serious way. In addition to the product, everything from the advertising and the visual merchandise to the sales staff define a luxury brand."

Loubier explains: "It's not just about having a history or heritage, but about using it to make a brand all the more pleasing to the tastes of people. You create to give your brand a point of difference. If a brand's DNA is based on just the need of the consumer it's not enough. It's a team effort - I like to think of it as a triangle between the president or CEO, designer and the merchandiser. When this triangle is good it meets the audience and public on what they want."

Naturally, the most successful brands are those that have their eye on the future, while creating a foundation for those that will be left behind.

If history has proven anything, it's that a brand with a strong identity coupled with a talented designer should always be able to survive.

"Heritage cannot be stopped - what you do every day is part of the heritage - but it also has to be passed on." Loubier says.

"The successful maisons are run by designers who have the feeling that they are not the owners, but more members of a virtuous chain that makes up the brand. Yes, you are responsible for much of what happens but eventually you need to pass it on."

Imagine a world without Karl, Marc or Phoebe. We match the industry's up-and-coming professionals with our favourite brands.

WHO: Raf Simons at Christian Dior
SUCCESSOR: Paris-based Chinese couturier Yiqing Yin
WHY: Yin's elaborate yet edgy style combines loose, free-flowing forms with armour-like structures to create modern pieces that Simons would approve of.

WHO: Rei Kawakubo at Comme des Garçons
SUCCESSOR: Paris-based duo Aganovich
WHY: It's Aganovich's mission to propose a new way of dressing for women by using a more cerebral and intellectual approach to fashion that Kawakubo coined in the 1980s.

WHO: Yohji Yamamoto at Yohji Yamamoto
SUCCESSOR: Shanghai-based Uma Wang
WHY: Wang's dark and deconstructed silhouettes are the perfect compliment to Yamamoto's work with their allblack palette and oversized shapes.

WHO: Phoebe Philo at Céline
SUCCESSOR: Bouchra Jarrar
WHY: The ex-Balenciaga designer is all about modern dressing. Her sleek lines would fit perfectly with Céline's minimalist sensibility.

WHO: Marc Jacobs at Marc Jacobs
SUCCESSOR: Edgy British designer J.W. Anderson
WHY: With his quirky and experimental aesthetic, he is Jacobs' British alter ego. Plus his new gig at Versace will give him plenty of experience at a top brand.

WHO: Donatella Versace at Versace
SUCCESSOR: Anthony Vaccarello
WHY: Vaccarello style can be summed up as molto sexy. His body-conscious silhouettes are accented with intricate details, such as bindings and cutouts. What could be more Versace than that?