The NEWSWEEK 50: Abu Dhabi's Emir Al Nahyan

Ruler of the tiny, oil-rich emirate of Abu Dhabi since 2004, Al Nahyan has something else the world is desperate for now: boatloads of cash, which he controls through the Abu Dhabi Investment Authority, the world's largest sovereign wealth fund, with assets of about $850 billion.

One of the oldest sovereign wealth funds (it was founded in the 1970s), the ADIA is publicity-shy. According to a recent study by the Monitor Group, the ADIA has made only 16 public deals in the past eight years. Of the $16 billion invested in those deals, $9.5 billion were in the financial-services sector, which has led some to question the investment judgment of the fund's managers. Still, as Monitor Group principal Drosten Fisher points out, "These types of funds have a very different time horizon for investment than many others. What's more, it's likely they've made a lot more investments in non-OECD markets that simply haven't gotten any press." With the exception of its high-profile deals, very little is known about where and how the fund invests.

That lack of transparency may become an issue. The ADIA already holds large chunks of U.S. firms like Toll Brothers, and the global downturn is fueling new buying opportunities around the world. While some of those deals will be in places like Dubai, the fund will likely keep looking for Western blue-chip assets, too. That's sure to test the tolerance of financial regulators and domestic political opinion, but in the end, the need for cash will probably win out.