They have four children apiece. They have razor-sharp brains with twin blades. They do not share an office but some people believe they share a brain. Their nickname is "the twins". All this translates into a marked ability to unnerve people, which is, of course, what makes them attractive as an interview subject. But what are they actually like?
We meet on a sweltering day at their temporary Neuilly-sur-Seine office base on the outskirts of Paris. They breeze into the room, late and apologetic, state-of-the-art mobiles ringing and beeping with messages. Famously disorganised, they are shepherded into line by Frederique, their assistant - shared, of course - for the past 12 years. News of their start-up, KR Media, has broken the day before, so the press is on to them.
It is only after a few minutes that you begin to get the hang of which twin is which. They are both short, dark and sharp-suited. Bruno is rounder than Eryck and, at first, does most of the talking. He is the younger of the two, 46 to Eryck's 48. Eryck comes across as more cerebral, more intellectual, the research one. Bruno is more bombastic, the trader. When I wondered how I'd distinguish their voices on the tape, Bruno said accurately: "As we agree on everything, we prefer to be quoted as one."
Their seismic departure from Aegis Group came via a short statement on 5 November last year. "Bruno Kemoun and Eryck Rebbouh are stepping down today as joint CEOs of Aegis Media Europe and as members of the Aegis board to pursue other professional interests."
As the owner of Europe's largest media specialist with a market share of about 12 per cent, Aegis had been a takeover target for as long as many people can remember. The departure of Kemoun and Rebbouh really set the hares running. For months, there were rumours about a growing rift with Doug Flynn, the gruff Australian chief executive of Aegis Group, the holding company for Carat and Aegis Research. The rumours were based on the twins' rare sightings of Flynn, and his forays into research at the expense, as they saw it, of the core media buying and planning business.
The twins' 24-year relationship can be traced back to the activities of two brothers, Gilbert and the late Francis Gross. They built Carat, and controlled the French media market for decades with an iron grip.
Kemoun and Rebbouh, also successful and driven Jews, were introduced to the secrets of the Gross brothers when they joined them in 1985. They launched 2010 Medias for the twins, and then the Carat brand via centres of expertise dedicated to each medium.
Kemoun and Rebbouh soon became the natural heirs of the Gross brothers and were initiated into the secrets of Gilbert's famous "black book".
This small, Hermes, leather-bound number was not only the best contacts book in European business and politics but also an intimate record of thousands of media deals. Gilbert's rates were disguised in illegible notes on one side of the page, the client ratecard on the other.
In 1993, with the Loi Sapin, the bottom fell out of the French media market. With it went Carat's opportunity to mint money by brokering to clients and enjoying legal year-end cash rebates from media owners.
Named after a French finance minister, the Loi Sapin brought with it transparency and prohibited Carat and others from receiving income directly from media owners. It forced them to compete on the qualitative parts of the process.
Carat France represented the destiny of Aegis. And their response to the Loi Sapin was a defining moment for Kemoun and Rebbouh. "It forced us to look at the future, to adapt our organisation in order to build the new model. We saw it as a chance to carve a new identity for Carat. As the rules of buying had vastly changed for everybody, the advantage of our size had no more effect. It pushed us to develop other specialised services like sponsorship and other types of businesses that delivered more service and generated more revenues from our clients."
In their mid-thirties, the pair faced their "perfect storm". The Loi Sapin forced them to shed staff by 40 per cent, from 500 to 300 in 18 months; recession reigned; and after the death of Francis Gross in 1992, Gilbert withdrew from the fray for a while. "All this put pain in a new context," Bruno says.
Now the pair are setting out on another course. After an intense courtship by the heads of the communications groups, they have opted to sell a minority stake (under 20 per cent) of their new European media network to Sir Martin Sorrell's WPP. He was on the phone minutes after their departure became public.
For months, it was thought that they would end up running Maxus, WPP's fledgling third media network. That, it is likely, was Sorrell's plan, but they want to control their own destiny: "We will work with WPP companies, leveraging Group M buying power and expertise in particular. Our partnership with WPP is key for servicing our clients internationally. We are close to Sorrell. But we want to be independent, to create a new European media network. That is our vision."
One can see why Sorrell would want the twins on side. Better to have the enemy inside than outside, after all. Who knows, Aegis may be on WPP's shopping list before long.
As for them, why pick Sorrell and WPP over John Wren and Omnicom? Why not go with John Dooner, who made the Interpublic approach, or Publicis' Maurice Levy? "All of the heads of the groups were charming and impressive. But Martin was the most proactive, the most personal, the most flexible and pragmatic," they say.
Does Sorrell's reputation as a micro manager worry them? "No, it's perfectly legitimate, it's our approach, too. All we care about is that we are back in the same market, the same battlefield and, by September, we will have the tools and the people to compete."
To date, they (and WPP) are the sole shareholders in KR Media, although they intend to offer equity to key managers as they expand. Is Mark Craze, the former chief executive of Carat in the UK, on their radar? "Mark is a friend, he's a great manager but not in our plans for the moment," they say.
Their vision is based on five or six European offices in the main markets, with "conviction, imagination and creativity" as the defining traits.
"We want to introduce a much more human factor into client relationships, to address the fact that the market has become too mechanical and process-driven. We don't advocate a media-centric position, but creative agencies are no longer alone at the top of the tree. Media has its part in creating competitive edge for brands."
But what has happened to the legacy of Carat's price reputation? And can KR Media ever hope to compete on price when they will be relative minnows? "It's not an issue. We will guarantee our clients the best productivity wherever required in Europe."
Make no mistake, they promise to deliver on price, in France and outside.
How? "In France, we will negotiate client by client, as it is the law. And outside France, WPP's Group M is first by volume so we will get the best prices."
Such muscle-flexing aside, it is obvious that leaving Carat was painful.
"That company was our flesh," they say. "There were 1,000 people at our leaving party, six weeks after we resigned, and that was the most emotional moment. We realised we were not just leaving the company but the people, too."
The pair are still Carat shareholders, though they have sold much of their stock and are bound by a non solicit clause until November. Even if they sell all their shares, as is likely, the emotional link with Gilbert Gross will remain. He is still a consultant to Carat and, for the time being, is tied to Aegis contractually.
But one day, who knows? They will not be drawn into specifics but big Carat clients such as Renault, LVMH and Danone will be on their wish list.
What's more, "the first advertisers who come to us will get a durable reward", they promise.
They may also hope to renew the link with the Gross dynasty. "We have links to Gilbert that will last forever," they say. "We feel enormous respect and gratitude towards him."
After the interview, the twins agree to answer more questions, by e-mail.
This is a ruse to prise them apart but they are wise to it. What is your idea of perfect happiness? "In business, being rewarded by our clients and our staff," they say, jointly. What is your most marked characteristic?
"Loyalty, and never being satisfied," they say, jointly. Which talent would you most like to have? "Punctuality," they chorus.
Exasperated, I lob over some more questions. What is your motto? This time their answers come in twos (hooray!) but they want me to guess who said what in reply (curses!). "It is not because things are difficult that we don't take risks, but because we don't take risks that they are difficult," one says. "The devil is in the detail," the other offers.
This game is repeated several times. In the end, like so many of their competitors over the years, I concede defeat. Look out Aegis, the twins are coming out to play.