Warren Buffett is 73 years old and his career as a stock market operator and investor now spans 62 years. He bought his first shares at the age of 11.

Buffett is a personal adviser to Arnold Schwarzenegger, the governor of California, and an economic adviser to Senator John Kerry, who may become the next president of the United States.

Buffett's success as an adviser and investor seems to know no bounds. He is also thought to be the second-richest man in the world, slightly behind Microsoft's Bill Gates - and he may well overtake Gates in the riches in the not-too-distant future.

Buffett's long career in the stock markets has not always been plain sailing, and there were times when his investment approach came in for severe criticism.

A case in point was the recent dot.com bubble. Buffett wanted no part in the market frenzy involving technology companies. His approach was ridiculed and many people suggested that he was out of touch and "just didn't get it".

At the time, Buffett said: "The fact is that a bubble market has allowed the creation of bubble companies, entities designed more with an eye to making money off investors rather than for them." He also called the frenzy over technology shares "a mass hallucination - by far the biggest in my lifetime".

It is also instructive to review Buffett's behaviour during an earlier period of market over-exuberance in the mid to late 1960s. Many of the participants in the market were newcomers, who were too young to have been hurt by the great crash of 1929 and the subsequent depression. This generation of speculators pushed the market to excessive levels.

Buffett's reaction was unusual. In 1960, Buffett said he could not find any undervalued companies, and so he dissolved the investment partnership he was running and returned the capital to the partners. However, Buffett retained his investment in Berkshire Hathaway, a textile company. He distributed Berkshire Hathaway shares to his former partners, along with a note stating that he would involve himself with running the company.

Berkshire Hathaway became Buffett's investment vehicle for a life-long investing career. It is now one of the largest and most profitable companies in the world.

Buffett's largest investments have been in insurance companies. Buffett's expertise in risk assessment and investing premiums goes some way to explain how what was once an obscure textile company has become a pre-eminent player in the insurance industry.

Over the past 12 months, Buffett's investment strategy has undergone an interesting change. Buffett said that until last year, he had never found it necessary to buy foreign currencies. However, by the end of 2003, Berkshire had $12 billion in foreign currencies (not US dollars). In May this year, Buffett noted that Berkshire had, since the year end, added "more than a little bit" to its foreign currency holdings. Although Buffett won't be drawn on which currencies he is buying, his strategy means he thinks the dollar's weakness will continue for the long term.

It becomes even more fascinating to watch Buffett's progress as his economic - and now political - influence grows each year.

Charles Ellis, a noted investment manager and writer, has this to say: "Warren Buffett is surely the greatest investor of this century - not so much because he built a great fortune within a free market as because he has shared his important thinking with us, and has openly demonstrated the sagacity and courage so vital to success. Berkshire Hathaway has been my largest, longest investment. Warren has been my best teacher."