With the impending retirement of Bill Gates from Microsoft comes an obvious question: How will history view him? As a founder of the world's most influential software vendor and one of the biggest creators of wealth ever? Or as a monopolist and digital robber baron?

In fact, Gates may be remembered less for any of that than he is for his philanthropic work - perhaps even as the greatest philanthropist the world has yet to see. Just like Andrew Carnegie, who today is remembered more for his charitable largess than his exploits in the steel industry, Gates' business legacy may fade over time in comparison to his work with the namesake foundation that he set up with his wife Melinda.

During the age of the industrial robber barons, Carnegie was an immensely controversial figure. In the 1870s, he founded Carnegie Steel, which became the world's largest and most profitable corporation. He became successful at least in part by paying very low wages, and by union-busting. For example, the infamous Homestead Strike of 1892 was set off when Carnegie cut the pay of his employees. The company hired replacement workers, and a small militia of Pinkerton detectives sent in to protect them killed and wounded numerous strikers.

After that incident, Carnegie was widely reviled. But in 1901, he sold Carnegie Steel to JP Morgan (who then turned the company into US Steel) and embarked on a massive philanthropic binge, giving away millions of dollars to libraries and educational institutions, and also funding scientific research and efforts to promote world peace. Ultimately, Carnegie gave away almost all of his money.

Gates likewise has said that over time, he will donate nearly his entire fortune to the Bill & Melinda Gates Foundation, which focuses primarily on improving health care, particularly in Africa and other parts of the developing world, and on reducing poverty.

Gates initially gave US$126 million to the foundation in 2000, and by 2006 he and his wife had given it more than US$26 billion. That made it the world's largest charitable foundation; as of this March, it had US$37.3 billion in assets, thanks also to donations by investor Warren Buffett, a friend of Gates who has said he plans to give a total of almost US$31 billion to the foundation.

Peter Krass, the author of a biography of Carnegie, thinks that the steel magnate's example likely made a significant impression on Gates' decision to devote most of his time to philanthropy after retiring from his day-to-day role at Microsoft at the age of 52.

"Gates said that he studied Carnegie, and so he has to have read Carnegie's famous essay on wealth," Krass said. In that essay, Carnegie concludes: "The man who dies thus rich dies disgraced."

"It looks as if Gates is following that Carnegie philosophy closely," Krass noted, while adding that the Microsoft co-founder is also hewing to Carnegie's model in another way, by being directly involved with the work done by the Gates Foundation. "Carnegie felt that he had to be hands-on with his philanthropy, because he believed that if you knew the best how to make money, you knew the best how to spend it," Krass said. "Gates apparently feels the same way."

Even so, Krass isn't sure whether Gates will be remembered more as a philanthropist than as the driving force behind Microsoft's success. "There are no businesses with Carnegie's name on them, but his name is on libraries all across the country," Krass said. "That's why he's remembered for his philanthropy. But 50 years from now, you'll most likely still be seeing Microsoft products. And the way Gates gives away his money, his name won't be on many buildings, so it won't be out in the public as much."