Meet one of the world's wealthiest investors

It was an opportunity too rich to pass up. Prince Alwaleed, one of the world's most successful investors and the wealthiest man in the Middle East, had invited me to spend a week with him in Saudi Arabia.

His objective: prove to Forbes that he is as wealthy as he claims to be. For years, the prince had told us he was worth several billion dollars more than the conservative estimates we printed in our list of the World's Billionaires, and he wanted to set the record straight.

The plan was for me to tour Alwaleed's vast real estate holdings, including his lavish Riyadh palace, meet with various executives of companies he owns, and gather other pertinent information needed to calculate his net worth for Forbes' annual World Billionaires list.

Last March, we estimated Alwaleed was worth $21 billion; he claimed he was worth more than $25 billion. This year, amid the massive decline of Citigroup, once his largest asset via his publicly traded holding company Kingdom Holding, Alwaleed's net worth had fallen, by our count, to $13.3 billion, making him the 22nd richest person on the 2009 list. Again, Alwaleed insisted he was worth more, despite serious threats to his fortune looming on the horizon.

But observing wealth on this scale, even for a seasoned billionaires reporter, was staggering.

I arrived in Riyadh in early October. After two days, my head was spinning. There was his impossibly large 420-room palace, decked out in marble and decorated with large portraits and photographs of Alwaleed, with two indoor pools and an indoor tennis court. It took an hour and a half to tour the whole place.

Then there was the 120-acre "farm and resort" at the edge of the city with its mini-Grand Canyon, mini-zoo, horse stables, five artificial lakes and multiple residences. It was a refreshing bit of green in an otherwise brown landscape. The prince evidently does not worry about water bills; one afternoon the sprinklers at the resort were going full tilt in the 90-degree weather.

Also on display: a fleet of 60 buff-and-green-colored cars and motor homes designed just for use at the prince's desert retreat. Another garage beneath the palace holds several dozen black cars--Range Rovers, Suburbans, Volvo SUVs and other vehicles used just for city driving.

And then came the jewelry. Upstairs at Alwaleed's palace in a wide marble hallway outside his bedroom, the prince's petite palace manager had lined the floor with 50 wooden boxes, each containing a lavish jewelry set fit for a king -- or in this case, a nephew of the king.

The most spectacular set on display was a diamond and emerald necklace with three emeralds the size of sparrow eggs dangling from the center, with earrings and a ring to match. With a combined total of 200 carats, the set is worth $40 million.

Most of the jewelry on display that evening was not to his wife's liking, he said, adding that Princess Ameera prefers less ostentatious sets. "It's too big for my wife," joked Alwaleed. "Plus you'd need to wear a very low-cut dress to go with it."

Then why buy the jewelry? "It's an investment. I paid $50 million for jewelry worth $150 million," he said, referring just to the swag by the bedroom. By Alwaleed's reckoning, his entire jewelry collection is worth more than $700 million.

One night I joined him and Princess Ameera and their staff on a flight to Cairo aboard his luxuriously outfitted Boeing 747. The main seating area of the plane has been transformed into a living room, with luxe couches along the plane walls, and behind it, a dining room where we ate a light meal prepared by the kitchen at the Four Seasons Hotel in Riyadh.

In Cairo, Alwaleed and his wife were among the honored guests at a charity dinner hosted by Egypt's first lady. Queen Rania of Jordan was there, and former U.K. Prime Minister Tony Blair was the guest speaker. Throngs of TV cameras filmed the honored guests.

Two nights later, back in Riyadh, Alwaleed and his entourage watched the recorded TV footage after dinner. It felt like the royal version of watching home movies.

Princess Ameera, 24, is wife No. 4 for Alwaleed; they've been married for four years. He's a one-wife-at-a-time guy, unlike some other Saudi men who may have as many as four wives at once.

Ameera, an engaging and attractive young woman whose passion is horseback riding, is studying for an undergraduate degree on a special program Alwaleed has arranged with University of New Haven. Professors from the U.S. teach Princess Ameera and several other young women in classrooms located within the prince's palace.

Alwaleed has two children with his first wife (a distant cousin); his son and a daughter are now in their 20s. His daughter Reem's extravagant wedding a few years ago, held at the ballroom of the Four Seasons Hotel Riyadh, was the talk of town. Transforming the ballroom into the lush setting for the wedding apparently took weeks; a clip of the scene, taken on a cellphone, even made it to YouTube.

Alwaleed became a grandfather last summer when both his son and his daughter each had their first child. One night while I was there, his daughter Reem came to the palace after dinner with her baby. The prince was clearly besotted with his adorable little granddaughter, kissing her and bouncing her on his knee.

The prince leads a very disciplined life. Each night he stays up until 4 a.m or 5 a.m., and sleeps for just four or five hours. The office hours at Kingdom Holdings, his investment vehicle, run from noon to 6 p.m. Around 8 p.m., the prince has what he calls lunch but what feels like dinner: a lavish buffet was set up outside in a different location each night, either at the palace, the resort or, on weekend nights (Wednesday and Thursday nights in Saudi Arabia) at his desert retreat.

He is practically addicted to text messaging. His phone is always at hand, and while I was there he sent text messages even while taking a bike ride and, out in the desert, while he was driving a big Suburban. His other near addiction: watching business news. During dinner each night, large flat-screen TVs were turned most often to CNBC.

Business news has been grim since last fall, but Alwaleed hasn't let it get him down. Stock of his Kingdom Holding fell 60% in the 12 months through mid-February, and has fallen another 19% in the last month, to a recent $1.03 a share in mid-March.

But on the evening of March 11, when Forbes released the World's Billionaires list, Alwaleed's office promptly issued a press release trumpeting his success, despite his falling fortune. "Prince Alwaleed ranked among the top 25 in 2009 Forbes Billionaires list despite global economic challenges."

When you're as rich as Prince Alwaleed, losing more than $7 billion in one year doesn't feel that bad.