If one London agency embodies the independent spirit and creative magic of British advertising in the past 30 years, it is Bartle Bogle Hegarty. This is the firm that, within months of its launch in 1982, demonstrated its creative credentials with brilliant, memorable campaigns that still resonate today.
Think of its very first work for Levi Strauss for its launch of black jeans. A solitary black sheep stood in a packed field of white sheep. "When the world zigs, zag," declared the ad.
Then there was the witty Vorsprung Durch Technik campaign for Audi, the erotically charged Lose control imagery for Häagen-Dazs ice cream, and, of course, that Levis ad featuring model Nick Kamen stripping to his underwear in a launderette. These were glossy adverts which often combined humour, music, irreverence and sexual energy and came to define an era.
For the co-founders of the agency, John Bartle, Nigel Bogle and creative supremo Sir John Hegarty, the black sheep captured their sense of independence and willingness to think differently, so they adopted it as BBH's company logo.
While other rivals sold out to big holding groups, BBH's founders retained their individual spirit and reputation for strong creative work, even when they sold a minority stake to the ad agency Leo Burnett, now part of France's Publicis Groupe, in 1997.
But yesterday that finally changed. BBH was sold in its entirety to Publicis in a deal that is thought to value the business at over £200m.
The agency would not discuss the sale price but annual revenues from BBH's seven offices, which include Brazil, are more than £120m.
The 53 partners in the agency are likely to collect more than £100m in cash for their 51 per cent stake.
It is a seismic moment for the British advertising industry — not least because Mr Bogle, 65, and Sir John, 68, will be stepping down from the day-to-day running of the agency. Mr Bartle had already left some time ago.
They didn't need to sell now, because they are already wealthy, but Mr Bogle said they felt "it was the right time", explaining: "It's always good to do this when you're in a very strong position creatively."
He is certainly right about that. BBH is resurgent.
It won more awards than any other London agency at last month's annual Cannes Lions, the world's most prestigious advertising festival. Among the agency's best work at Cannes was another erotically charged ad for Lynx deodorant, in which sparks flew, and a dramatic film for The Guardian newspaper, a twist on the Three Little Pigs nursery tale for the digital age.
The defining features of BBH's work are still on display 30 years on.
Mr Bogle admitted it had taken a long time – as much as two years – to agree the sale to Publicis Groupe.
He and Maurice Levy, the long-serving boss of Publicis, stressed that BBH has won a guarantee that it will retain its independence within the wider group, which also owns other agencies such as Saatchi & Saatchi, Fallon and Starcom MediaVest.
"A lot of effort has gone into ensuring this won't change BBH in terms of the values, the culture and the micro-network," said Mr Bogle, referring to BBH's seven offices, including New York and Los Angeles, which employ 1,000 worldwide.
"I think with a lot of agencies when the founders step back, the agency fades – that ain't going to happen with us," added Mr Bogle.
Sir John Hegarty was equally adamant that BBH's culture will continue after they leave.
"Creativity is at the very heart of BBH," he said.
"The quality of our work and the people who produce it have always been central to our success and will continue to be so into the future."
Sir John, in particular, has left a strong body of work that will be a touchstone for future leaders at BBH, just as he has already inspired a generation of creatives who have left BBH to head the creative departments of many other London agencies.
It was Sir John who came up with so many of the ideas at BBH like Vorsprung Durch Technik, a line that he happened to spot on an old piece of company literature during a visit to an Audi office in Germany.
Sir John realised that rather than disguise the carmaker's German roots, the car brand should celebrate them, and so an award-winning ad slogan was born.
Even now, Sir John, who likes to walk into BBH's Soho offices on Kingly Street from his home in Clerkenwell, still retains a tremendous passion for advertising and ideas.
"The other day, I saw a man cycling with a dog in his basket on the front of the bike," he told me in an interview last year.
"He was turning left and the dog stuck out his paw too and I thought that's a funny image, I'll use that one day. I was the only person to see that."
Sir John is not sentimental, however. For him, great advertising isn't just magical. He believes it should communicate a fundamental truth about the brand and, crucially, that it should drive sales.
"Advertising is a great window into a business," he said. "Is it consistent? Is it confident? Does it communicate? If I were an analyst in the City, I would be asking companies, 'Why do you keep changing your advertising?'"
One of the hallmarks of BBH's 30-year history is that it has been so consistent.
There have been a few hiccups, such as when the agency parted ways with Levis in 2010 after 28 years, but even then there was a principle at stake as BBH felt it was no longer producing great work for the brand.
BBH proved it could bounce back, with such diverse campaigns as the rapping farmers for yogurt brand Yeo Valley and clever poster ads for Google that played on the phonetic spelling of words in the website's "search box".
The BBH sale is just the latest in a wave of acquisitions of London advertising agencies.
WPP bought Farringdon-based digital agency AKQA in an estimated £350m deal in June and US giant Omnicom paid around £55m for Adam & Eve, the Covent Garden agency behind the John Lewis adverts.
But in terms of symbolism, the Bartle Bogle Hegarty sale is bigger. Why? Because this sale marks the end of an era.
BBH's greatest hits
1982 John Bartle, Nigel Bogle and John Hegarty found BBH
1982 Levi launches black jeans with "When the world zigs, zag"
1982 Audi's Vorsprung Durch Technik campaign
1985 Levi's Launderette ad with Nick Kamen
1991 Häagen-Dazs ice cream launches in Britain with its Lose control campaign
1997 BBH sells 49 per cent stake to Leo Burnett (later part of Publicis)
1999 Levi's Flat Eric ad
1999 Johnnie Walker whisky's Keep Walking campaign
1999 Vote Gail – projects image of model Gail Porter on to Big Ben for FHM magazine
2005 Wins British Airways account
2010 Levi ceases to be a client
2010 Yeo Valley yoghurt's "rapping farmers" ad, taking entire ad break during X Factor
2012 Most-awarded London agency at Cannes Lions advertising festival
2012 Sells remaining 51 per cent stake to Publicis