(FORTUNE Magazine) – ANY SELF-RESPECTING ADMAN would hop on the first plane to Seoul to win a $400 million account from Samsung. But how many would fly in from London for 24 hours just to attend a museum opening? If you're WPP chief Martin Sorrell, and the family behind Samsung has financed the museum, you do just that--especially if other ad execs won't be there. Since Samsung put its advertising and marketing business up for review in March, Sorrell has trekked to South Korea four times, eating kimchi with Samsung execs, blasting them with relentless e-mails at all hours, and hoping his sheer bloody-mindedness enables WPP to outmaneuver rivals like France's Publicis and American giants Omnicom and Interpublic Group.

A decision by Samsung could come within weeks, and if WPP is victorious it will be a testament to just how persuasive Sorrell's one-on-one lobbying can be in winning clients.  And if WPP loses, well, it won't be for lack of trying.  "Martin can be quite persistent," says HSBC marketing director Peter Stringham, who chose WPP to run his company's $600 million global advertising and marketing campaign after a similar bake-off earlier this year. "He was there from the first meeting to the last. He'd pitched to us a couple of times before and not gotten the account, but he'd had his eye on it for years."

The HSBC win is just one of a series of successes in recent months that have catapulted WPP ahead of most of the competition. In early November, its MindShare division won a deal to manage Unilever's $1.3 billion European media account. And earlier this fall WPP agreed to buy Grey Global Group, one of the last remaining large independent ad firms, for just over $1.5 billion. With the addition of Grey, analysts estimate, WPP's combined revenue of $10.3 billion will place it just a few hundred million dollars behind Omnicom, which leapfrogged over WPP in the late 1990s to become the leader in the advertising and marketing world.

After surviving a severe financial crunch in the early 1990s and the ad recession a decade later, Sorrell is back, tweaking rivals and plotting potential acquisitions. Revenue for the third quarter of 2004 showed the biggest increase in four years, and analysts expect 2004 net income to rise 15%, to $706 million. Sorrell is consumed with the company's growth. "WPP isn't a matter of life or death for me--it's more important than that," he says, echoing the words of a legendary British soccer coach. "I'm not a manager, I'm a founder. WPP is a part of me, and I take a personal interest."

The two major trends roiling Madison Avenue today--clients demanding a broad range of services from one parent company, while shifting resources from traditional advertising to direct marketing--both play directly into WPP's strengths. At the same time, the consolidation in industries like banking, media, and consumer goods favors Sorrell's more efficient one-stop-shopping approach, since WPP offers everything from traditional ad design to market research, PR, media buying, and direct mail.

The Grey acquisition won't close until early next year, but Sorrell is already eyeing pieces of the foundering French ad giant Havas. Whether or not a deal comes to pass, his company has a good chance of overtaking Omnicom on the basis of organic growth and regaining its position as the biggest marketing and advertising company in the world. "Martin is absolutely ruthless about becoming No. 1," says one WPP ad agency exec. And while Omnicom's shares have performed far better than WPP's since Sorrell took over in 1986, WPP, traded on the London and New York exchanges, is slowly catching up. Over the past two years its stock has jumped 47%, well ahead of Omnicom's 34% gain.

One key to WPP's success has been Sorrell's ability to get the disparate parts of his sprawling empire--ad agencies like Ogilvy & Mather and J. Walter Thompson; media strategists such as MindShare; and direct marketers such as Wunderman--to work together to woo clients. Sorrell and other consolidators have been talking about synergies in the business for years, but for the first time there's evidence that having a wide array of services under the WPP umbrella is an asset rather than an organizational and managerial headache. Indeed, to win HSBC's business, Sorrell put together a team from across WPP instead of relying on one agency to make the pitch--a first for his company.

What's more, he has positioned WPP to capture a bigger share of the less sexy but faster-growing parts of the business that advertising types call "below the line"--direct mail, market research, public relations, promotional events, and Internet marketing. These services lack the glamour of made-for-TV advertising. But while the traditional business of crafting a 30-second spot sputters along at a 2% to 3% pace, below-the-line sales are growing at twice that rate. "WPP's strength is below the line, and they've been really forward-looking," says Bear Stearns analyst Alexia Quadrani. "Martin really believes the world is going toward more direct marketing and that pure advertising will be less important."

IN AN INDUSTRY populated by shameless schmoozers, the 59-year-old Sorrell is in a league of his own. "It doesn't matter what time it is," says former Viacom CEO Mel Karmazin. "If Sir Martin didn't get back to me in 15 minutes, I'd call to see if he'd been injured." Sorrell is the same way with reporters and analysts--he seems to enjoy the spotlight and the give-and-take. Yet for all his accessibility, his persistence and aggression can rub people the wrong way. Before Sorrell bought his company and won him over, Ogilvy & Mather founder David Ogilvy described Sorrell as "odious." And when Sorrell won a bidding war for Grey in September, bested Havas CEO Alain de Pouzilhac saluted him as a master at "manipulating people."

Sorrell comes across in person as confident, witty, and a tad arrogant, talking rapidly about the future of advertising and the challenges of keeping fractious clients and ad agencies happy. "Growing a big company by 5% to 10% consistently is a big job and difficult to do," he says, sitting in the tastefully appointed London townhouse where WPP has its headquarters. "But if it were easy, my cocker spaniel could run the company." Although Sorrell favors the traditional suits and cuff links typical of London execs, he's not flashy in his dress or personal style. His favorite activity is networking with clients and media types. A father of three boys--all now investment bankers, not admen--he has been married to the same woman for 33 years. Sorrell may be a favorite of the business press, but he's not a fixture of the society columns.

In London, where Sorrell grew up as the son of a successful radio and TV retailer before attending Cambridge and Harvard Business School, there is still some resentment that this parvenu has a $175 million fortune, not to mention a knighthood. The Financial Times described him as "not overly concerned with social niceties." British newspapers delight in spotlighting his pay--$3.9 million last year, not much by U.S. standards but considerably more than rival industry bosses. And there was more than a little satisfaction when the ad recession and the dot-com bust sent WPP's stock plunging from $100 a share in 2000 to $30 in early 2003.

But Sorrell seems to delight in defying the skeptics and the snobs. After a decade as the financial mastermind behind the rise of London's Saatchi & Saatchi ad firm (he was nicknamed "the third brother" alongside Charles and Maurice Saatchi), he struck out on his own in 1985. He bought up shares and secured control of a London-listed basket manufacturer, Wire & Plastic Products, using it as an acquisition vehicle to buy Ogilvy & Mather and J. Walter Thompson in the late 1980s. This debt-fueled acquisition binge brought WPP to the edge of bankruptcy when business slowed in 1992, but banks like J.P. Morgan and Citibank allowed Sorrell to weather the storm, swapping debt for equity in WPP. By the end of the decade he was back in merger mode, buying Young & Rubicam for $4.7 billion in 2000, the largest acquisition in advertising history. And despite the steepest industry downturn in decades, he followed up the Y&R purchase with more deals, scooping up media buyer Tempus in 2001 for $700 million and Britain's Cordiant Communications for $490 million last year.

In his 36-year career, Sorrell has never designed an ad or written copy, but he's not put off by the industry's habit of venerating creative legends like the Saatchis while disdaining financial types. "I may be a bean counter, but I'm not an accountant," Sorrell says, and in WPP's most recent annual report, he poked fun at his reputation with a cartoon-like spread featuring lima, kidney, and pinto beans. "I have views on advertising," he adds, but when it comes to getting involved in the creative process, "it would be fatal if I did that. I regard myself as a businessman."

Maybe so, but Booz Allen Hamilton exec and veteran industry observer Randall Rothenberg says Sorrell is also a throwback to the era when leaders of the advertising world were considered captains of industry alongside the CEOs they created campaigns for. "Sorrell is arguably the last and only statesman in the business," says Rothenberg, comparing him with figures like Leo Burnett, who appeared on the cover of Time in 1962, or Chester Bowles, who went on to become governor of Connecticut. Indeed, Sorrell is happy to hold forth with Clintonian gusto on topics as varied as the potential of the BRIC countries (Brazil, Russia, India, and China), tensions between the Muslim world and the West, or the dangers of the worsening U.S. trade deficit. "It's been decades since advertising execs had that kind of standing," says Rothenberg, "but Martin really aspires to be more of a global business leader than an adman."

SORRELL BARELY SLEPT on the flight back from his first Samsung pitch in Seoul last spring. He was using the phone on board, dictating e-mails to his secretary in London. Early the next day, he donned a gray morning coat to play a British business mogul in a skit that was part of WPP's final pitch to HSBC. The shtick was witty and included a chauffeur named Maurice (as in Publicis CEO Maurice Levy, a Sorrell nemesis).

The pitch worked. But what made the win really sweet was more than just securing a $600 million account or taking the business away from Publicis, one of the incumbent HSBC agencies. Instead it was significant because HSBC was the first major client to directly approach the four major ad-holding companies that dominate the business--WPP, Omnicom, Publicis, and Interpublic--instead of their individual agencies. HSBC's goal? Consolidating an entire marketing budget with one provider and gaining the economies of scale that big companies seek in every other line of their business. Besides cost-savings, HSBC was also looking for something more elusive--a unified approach to driving the HSBC brand, rather than the old scattershot approach. HSBC marketing boss Stringham says that when he joined the bank four years ago, he "found it extraordinary that we had a global ad agency but still had hundreds of agencies doing below-the-line work. Think of how many account people that is, knocking on doors every day."

Samsung is the second client to demand this approach, and Sorrell believes the trend may mark the industry shift he has been waiting for since he launched WPP two decades ago. "The new superagencies have a major opportunity," he says, and that means trouble for midsized firms that don't offer a range of services. "The middle of the road is clearly becoming an increasingly difficult place to be, with traffic approaching from both directions."

And there is evidence that WPP is taking share from the competition. "WPP is doing extraordinarily well in terms of winning large customers right now," says Sanford Bernstein analyst Michael Nathanson, citing the $3.2 billion in new billings that WPP won from clients like HSBC, Unilever, and Nestlé in the first nine months of the year. Last year, WPP had a 15% global share of the advertising business, up from 14.1% in 2000. With Grey, its share will hit 18%, putting it about even with Omnicom. With global advertising spending expected to grow only 4% to 5% over the next two years, Nathanson says, "The only way to really grow today is by taking market share, and that's what WPP is doing."

The same consolidation driving WPP's gains in more traditional areas is also boosting its share of the fast-growing business of planning and buying ad campaigns for clients, says Irwin Gotlieb, CEO of Group M, a WPP global media-buying company. When Gotlieb won the Sears account in 2000, he says, Sears had three agencies buying its spots. Today, all of the retailer's $785 million in ads are bought for it by Group M. Besides lowering overhead, choosing one media buyer also gives advertisers more leverage when it comes time to negotiate rates with broadcasters and publishers. And with the Grey acquisition, WPP will have a 29% share of the worldwide media-buying market, compared with 21% for Publicis, 17% for Interpublic, and 15% for Omnicom.

Group M and its MindShare unit have also pushed the boundaries of what's thought of as media buying and planning. For Sears, MindShare worked with ABC to develop Extreme Makeover: Home Edition, in which a troubled family's home is renovated from top to bottom. Everyone comes out a winner--the audience's heartstrings are pulled, the family gets new digs, and all the featured products used to fix up the house are from Sears. What's more, cast members from the show appear in the Sears ads that run between segments. Even better for Sears, MindShare was able to secure a prime-time Sunday night slot for the program. Similarly, it wasn't a coincidence that AT&T provided the lifeline on Who Wants to Be a Millionaire--Group M's Mediaedge:cia developed the idea for AT&T and handled the negotiations with ABC. "It's not just about content integration or product placement," says Gotlieb. "It's also a way of mitigating the rising cost of buying traditional ads."

The rising cost of TV time--the price of a 30-second Super Bowl spot has doubled to more than $2 million since 1996, despite fewer viewers--is also spurring WPP's below-the-line business. So is a conviction among clients that direct mail, Internet promotions, and other nontraditional approaches are more effective. A decade ago, says American Express chief marketing officer John Hayes, nearly 80% of Amex's ad dollars were spent on TV ads. Today, the tube accounts for about 35% of the company's ad spending. That's a dramatic shift, but Ogilvy & Mather, Amex's longtime agency, managed to adapt and retain the business. Ogilvy and the rest of WPP, Hayes says, "have been ahead of the industry in terms of anticipating and getting up to speed on what's happening." Ogilvy & Mather CEO Shelly Lazarus says this year marks the first time her agency will get more of its revenues from below-the-line work than from creating TV, print, or radio ads. "It's gone faster than we would have thought," she says. "Traditionally, below the line was 20% to 30% of our revenue, and our goal was to make it half by 2007. We were a bit surprised."

Although Ogilvy has been successful at retaining clients, not every WPP agency is thriving. Following WPP's expensive acquisition of Y&R in 2000, the firm experienced a loss of top talent and the departure of key clients such as United Airlines and Kentucky Fried Chicken. Even worse, former Y&R president John McGarry set up a boutique that's now competing with Y&R for business. So while individual Y&R units like direct marketer Wunderman are thriving, Y&R's traditional advertising shop is struggling. CEO Ann Fudge came aboard 18 months ago to help turn the firm around, only to watch Burger King take its $250 million in billings to another agency. This summer Fudge shook up Y&R's management structure, but despite the turmoil Fudge insists Sorrell is behind her. "I appreciate the support he's given me in this role," says Fudge, adding, "I'm here to turn this baby around, no matter what it takes."

Besides Y&R, another worry for WPP shareholders is that Sorrell will go back on the acquisition trail. His past deals have proven smart in the long run, but using WPP's stock as currency tends to depress the share price. Although Sorrell denies he's eyeing a Havas buyout, analysts who know his habits say anything is possible with a serial acquirer like Sorrell. "I hope the acquisition spree is coming to an end," says Nathanson. "They've operated very well in the last two years. We want to see more disciplined use of capital, and the hope is that WPP will keep reaping the benefits of the investments they've made."

Even if the advertising market in North America and Europe weakens, WPP is likely to get a boost from Asia. Sorrell is passionate about the region's potential and says that Asia and other emerging markets will generate one-third of WPP's revenue within ten years. Although Asia contributed only 15% of WPP's revenue in the first nine months of the year, the region is by far the fastest growing, clocking a more than 15% gain in sales. WPP already is the market leader in China, South Korea, and India, and under the direction of Group M's Gotlieb, who was born in China and is fluent in Japanese, WPP has carved out a 32% share of media-buying business in Asia. While only about 10% of Chinese consumers can afford the products WPP's clients are selling, Sorrell says, "even they represent one-half of America." And that emerging middle class is expected to double before too long.

Will WPP ever be big enough? With typical Sorrell spin, he says his goal has never been to be the biggest but to be the best: "We've got 70,000 people. Do we need another 70,000?" Of course WPP doesn't. But given Sorrell's appetite and ego, he probably has his next deal--make that two deals--already figured out.