For seven years Warren Buffett, the so-called Oracle of Omaha, ranked just behind his good friend and bridge partner Bill Gates as the world's second-richest man. That era is over, at least temporarily. On March 29, Mexican telecom titan Carlos Slim Hel� quietly slipped past the value investor.

As of market close on Wednesday, Slim is worth $53.1 billion, compared with Buffett's $52.4 billion. He is also breathtakingly close to passing Gates, currently worth $56.0 billion. Gates, who co-founded Microsoft in 1975, has been the world's richest man for a record 13 years.

Slim added $4 billion to his fortune in the two months since we locked in net worths for our annual billionaires rankings. His second-largest holding, Carso Global Telecom, which controls ubiquitous fixed-line operator Telmex, has jumped 15% in that time.

• In Pictures: The World's Billionaires
• In Pictures: Celebrity Billionaires
• In Pictures: Bachelor Billionaires
• In Pictures: Billionaires Under 40

His biggest holding, wireless operator America Movil, is up 4% since it announced earlier this month that it was in talks to buy a third of Olimpia, the holding company that controls Telecom Italia.

By contrast, Buffett's Berkshire Hathaway shares have slipped slightly.

Slim's latest gains continue an amazing run for the 67-year-old tycoon. He has added $23 billion to his fortune over the last 14 months. The surge has been fueled largely by a strong Mexican economy and a stock market that jumped 49% in 2006.

The Mexican magnate's rising fortune has caused a good deal of controversy because it has been amassed in a nation where per capita income is less than $6,800 a year and half the population lives in poverty.

Critics claim he is a monopolist, pointing to Telmex's control of 90% of the Mexican landline telephone market. Slim's wealth is the equivalent of roughly 7% of Mexico's annual economic output. If Gates had a similar proportion in the U.S., he'd be worth $874 billion.

Slim says he is unfazed by the criticism. "When you live for others' opinions, you are dead. I don't want to live thinking about how I'll be remembered," he said earlier this year. He also claims indifference about his ranking and says he has no interest in becoming the world's richest person. When asked to explain his sudden increase in wealth at a press conference soon after our annual billionaire rankings were published, he reportedly said, "The stock market goes up ... and down," and noted that his fortune could quickly drop.

• In Pictures: Billionaire Dropoffs
• In Pictures: Richest Newcomers
• In Pictures: Billionaire Biggest Gainers

These days, Slim insists his biggest concern is using his wealth to help solve Mexico's social ills. A year ago he infused one of his foundations, which had been long neglected, with $1.8 billion. In the fall he pledged to donate up to $10 billion to health and education programs over the next four years.

Still, he poked fun at his American counterparts' much-ballyhooed philanthropic efforts at a recent press conference. "Poverty isn't solved with donations," he reportedly said, adding that building businesses often does more for society than "going around like Santa Claus."

(Above) Carlos Slim Helu. Photograph: Susana Gonzalez/AFP/Getty Images

• In Pictures: Billionaire Divorcees
• In Pictures: Billionaire Women We Envy