NEW YORK (FORTUNE magazine) - Lots of executives like to think of themselves as relentless. But Bob McDonald defines the word.

While growing up in Arlington Heights, Ill., he decided that he would attend the U.S. Military Academy at West Point. Like thousands of other applicants, he contacted his Congressman requesting a recommendation. He was 11 at the time. Not wanting to disappoint the youngster, the Congressman told him he could take the civil-service exam annually until he reached his junior year of high school, the official age of West Point applicants. So McDonald did just that, taking the test some six times before he was finally admitted at 17. "Hard work pays off," he says.

Bob McDonald, Procter & Gamble

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His Congressman, who happened to be Donald Rumsfeld, went on to run the Pentagon. McDonald finished 13th in his West Point class, served as an Army captain in the 82nd Airborne, and in 1980 joined consumer products giant Procter & Gamble (Research), where he was determined to work his way up the corporate ladder. After spending two decades rising through P&G's cleaning and laundry divisions (Dawn, Cascade, Tide), he was tapped to run the multibillion- dollar northeast Asia region. (For those keeping score, A.G. Lafley, P&G's superstar CEO, ran all of Asia shortly before getting the corner office.)

If Lafley, 58, ever retires, P&G watchers say McDonald, 52, and now the company's vice chairman of global operations, is on the short list of candidates to take his place. "He is smart. He is serious. You can just read in his face how desirous he is to be an asset to this company," says Xerox CEO Anne Mulcahy, who counts McDonald as a trusted board member.

Inside P&G, McDonald, who calls himself a "voracious observer," is known as a shrewd brand builder and a straight-talking nice guy. Does he want the top job? "I don't think I would turn it down, but it is premature," he says. "I have my hands full." Indeed, he currently oversees everything from customer marketing to sales, IT, and developing-country strategies.

When Lafley took over the $67.9 billion company five years ago, "we were probably reaching two-fifths of consumers," says McDonald. "We changed our strategy to focus more on developing markets and low-income consumers, and today we're reaching three-fifths of the world's consumers. But for P&G to really be successful, we want to reach all of them." Clearly, the guy thinks big.

If the list of leadership tips he carries with him at all times is any evidence (No. 1: "Everyone wants to succeed"; No. 2: "Success is contagious"), the "s" word is never far from his mind. The company says the 58-year-old Lafley is not going anywhere anytime soon, which is just fine. McDonald will be waiting -- unless someone poaches him first.