Bill Weldon remembers talking to his wife about problems in the US housing market long before the credit squeeze set in. The chief executive of Johnson & Johnson had been perplexed for some time by the number of people who were over-extending themselves by taking on large mortgages - a trend distinctly at odds with his self-confessed prudence.

"My wife and I are just very conservative people," he says in an interview with the Financial Times in his modest, almost under-furnished, office.

This could be dismissed as scripted false humility. After all, Mr Weldon earns a lot - nearly $5m in salary and cash bonus in 2006 of total compensation valued at $28.6m. But the cautious approach to his own finances is reflected in the way he runs the world's largest health group.

With a market value of $195bn and forecast revenues of $65bn for this financial year, the health conglomerate has few financial restraints. Yet two years ago J&J allowed an agreed bid for Guidant, a medical device maker, to be broken up by a much smaller rival, Boston Scientific, which paid $27bn.

Mr Weldon defends his decision to stick to J&J's $24bn offer as good sense. "If you want to be bold and brazen you could pay whatever you want to get it. But I'm not sure it ever returns value to shareholders. If we couldn't return value to shareholders, we weren't going to do it," he says.

It is often hard to tell where Mr Weldon stops and J&J begins. Perhaps this is not surprising as the down-to-earth, square-jawed, 59-year-old has spent his entire 36-year career at J&J, an icon of corporate America.

Dressed casually in a light sweater and leather loafers, Mr Weldon is straightforward, competitive and prudent - like an old-fashioned sports coach.

"Your personality changes as you evolve," he says. "I am a very very competitive person. And people know that I want us to play to win, and don't want us to play just not to lose."

Born in Brooklyn, New York, not far from J&J's global headquarters in New Brunswick, New Jersey, Mr Weldon had not planned a career in management. In fact, he vowed after working one summer as a junior accountant that he "would never go into business". His ambition was to enter medicine.

Just before graduating from Quinnipiac University in Connecticut, his wife became pregnant with the first of their two children. So he decided to get a job at J&J to pay some bills as the pressures of fatherhood approached. A family friend who had promised to pay Mr Weldon's medical school fees died and his medical ambitions were thwarted. "He passed away and I never left J&J," Mr Weldon says.

Now, after almost six years as J&J chief executive, Mr Weldon is considering his legacy. It is a daunting thought in view of the company's history, which has seen compounded annual sales growth of more than 11 per cent since it was founded in 1887.

Increasing scientific, regulatory, pricing and cost pressures have added to the task facing for Mr Weldon, who has restructured J&J, cutting 4,000 jobs, in an effort to keep the company's profits growing robustly in the next two potentially difficult years. But while J&J is financially cautious, it is also obliged to think big and "experiment with new ideas", as stated in the Credo it set out more than 60 years ago. This statement of guiding principles prioritises customers, doctors, nurses, patients, mothers and fathers; second, employees; third, helping the community; and last, stockholders who on serving the others "should realise a fair return".

Mr Weldon believes his biggest impact may be on the company's approach to innovation, though he adds: "I may not be alive to see it happen." In the short term, he is pushing J&J's healthcare companies to share ideas and expertise so they can invent products and sell them more efficiently. There are 80 projects in converging technologies, of which about six, he suggests, could be chosen for fast-track development. One involves J&J's contact lens business working on a lens that delivers a drug directly to the eyes.

And in spite of the failure to buy Guidant, which makes implantable devices that use electrical signals to control heart rhythms, Mr Weldon remains fascinated with medical devices. He plans to continue to seek microelectronics expertise and sees no end to the possibilities of medical devices.

"I think the device industry is an extraordinary place to be," he says. "Some day, some way, you're going to be sitting in New York and the surgeon is going to be performing surgery [on you] from the west coast."

Nearly every conversation reveals his enthusiasm for healthcare technology. In November, Mr Weldon made a move he hopes will help J&J shape the industry's future, setting up a group with the Orwellian title of the Office of Strategy and Growth to research futuristic possibilities in healthcare.

The blue-sky team is charged with identifying as-yet unimagined lines of business, including information technology and potential future partners such as Google, Microsoft and Cisco. "Who knows who it is going to be? It is trying to understand the future of healthcare - totally divorced from where we are today," he says.

In another example, Mr Weldon speaks of how J&J's decentralised business model and diverse product portfolio have allowed it to thrive while other rivals, particularly the big drugmakers, are seeking ways to transform themselves.

"I don't think there's any company positioned as well as we are. There's nobody that has the size and financial strength to be able to do this."

A high school football injury has finally caught up with Mr Weldon, so that he walks a little stiffly now. The knee was replaced two years ago with a titanium implant but it is a constant reminder of Mr Weldon's days as an athletic, aspiring doctor who detoured to become a J&J salesman. And it is a knee made by J&J's DePuy, of course.

He implies he has no regrets, arguing that his current role gives him the chance to help more people than if he had fulfilled his ambition to become a doctor.

And, he insists: "I'd say I am the same person I was 30 years ago."

'Take the heat for the failures and give credit for the successes'

Bill Weldon has a healthy sense of humour, not least about the role he has carved out for himself at Johnson & Johnson. Asked about the task of managing the decentralised conglomerate - in which divisional executives are given a high level of control - prompts a self-deprecating laugh.

"I'm still trying to figure that out sometimes," he jokes, leaning over to grab his coffee mug. "My son says I just sit around and drink coffee and go to meetings."

Mr Weldon paints a picture of his day-to-day job as that of a team coach freed to see things others miss. In his view, his task is to emphasise and plug holes in strategy, and push the development of his team members, who will ultimately decide the outcome for J&J.

"My role is to take all the heat for the failures and give all the credit to everyone else for our successes ... to help look at some of the things we may want to break out and give more attention to," he says.

For instance, he points to J&J's official partnership at the Beijing 2008 Summer Olympics to help future business in China, and push for a huge emphasis on emerging markets for all the businesses.

Sometimes, he says, his responsibilities prompt controversy. Last year, J&J did what Mr Weldon calls "the last thing we wanted to" by suing the Red Cross, claiming it violated the company's long-standing trademark red cross brand on consumer health products.