The 10 Most Powerful Billionaires

1 Bill Gates $40.7 billion Rank: 1

Microsoft's operating software drives 93% of the world's desktop computers.  The world's richest man is also its biggest giver: more than $1 billion annually, much to vaccine research.

2 Warren Buffett $30.5 billion Rank: 2

The Oracle of Omaha owns 36% of Berkshire Hathaway, a property/casualty company with an immensely profitable sideline managing its portfolio of stakes in blue chips like Gillette, Coca-Cola. Vows to leave his wealth to charity.

3 Silvio Berlusconi $5.9 billion Rank: 45

Italy's prime minister owes much of his influence to Fininvest, his investment firm that owns 49% of Mediaset, Italy's largest television network. He also has  interests in banking, insurance and publishing.

4 Rupert Murdoch $5.5 billion Rank: 54

While rivals circle the drain, Murdoch's News Corp. remains buoyant on hits  like Fox TV's Joe Millionaire. The media baron's empire also includes  movies and publishing, but satellite television gives him his global  reach. He hopes to have better luck in the second round of his prizefight  for satellite broadcaster DirecTV.

5 Li Ka-shing $7.8 billion Rank: 28

Centered on the conglomerate Hutchinson Whampoa (telecom, port services, real estate), Li's empire spans 41 countries and accounts for 13% of Hong Kong's stock market value. Asia's richest man has invested $7 billion in Mainland China and built 400 miles of roads and bridges.

6 Prince Alwaleed $17.7 billion Rank: 5

This Saudi prince's influence reaches far beyond the Middle East.  Citigroup's largest individual investor has met with heads of states of more than 20 countries, including Russia, the U.K. and China.

7 Mikhail Khodorkovsky $8 billion Rank: 26

Head of Russia's second-largest oil company, Yukos, helps  keep world energy prices down by boosting oil exports in face of OPECprotests. Russia's richest man is also leading  the charge in making the country's murky business affairs more transparent.

8 Robson Walton $16.5 billion Rank: 7

Eldest son of Sam Walton controls family's 38% stake in Wal-Mart,  the world's largest retailer: some 3,200 stores in the U.S., nearly 1,200 stores abroad. Sales: $244 billion. The company might beef up its European presence with a bid for U.K. grocer Safeway.

9 Carlos Slim Helú  $7.4 billion Rank: 35

Known for his investments in U.S. retailers like Saks and Circuit City, Helú also has holdings representing a third of the Mexican Bolsa. He is plowing millions into rejuvenating Mexico City and has hired Rudolph Giuliani to curb the city's crime. He is also tight with Mexico's top political up and comers.

10 Azim Premji $5.9 billion Rank: 45

Owns 84% of Bangalore-based Wipro, India's largest technology concern. Wipro is a leader in the lucrative business of shifting white-collar jobs from the U.S. and Europe to Asia.