Who has more power and success than a world-famous actress? Simple: one who also has a successful music career, clothing label, line of perfume and restaurant. Better yet: someone with all these things who's also very young.

No one knows this better than musicians these days. While movie and television stars have been branching into retail and licensing for decades--consider Elizabeth Taylor's fragrances and Cheryl Teigs' line for Sears--musicians are now leading the celebrity retail push.

• In pictures: Hollywood's Moguls In The Making
• In pictures: The Most Overexposed Celebrities

"I think musicians need to look for more sources of income. The old record and CD business has pretty much disappeared," says Michael Stone, president and chief executive of The Beanstalk Group, a brand licensing agency and consultancy. "Musicians are looking for other legs of their marketing table so that they can have a broader career."

Expanding into several industries is de rigueur. "It's not just important--it's imperative in this market," says Howard Bragman, a public relations executive and the author of the upcoming Where's My Fifteen Minutes? "You got this brand, and it's got a personality and you have to get as many income streams as you can."

That's why Curtis Jackson, aka 50 Cent, was at the top of our list of Hollywood's moguls in the making. Thanks to some savvy investing, Jackson's stake in VitaminWater earned him nine figures when Coca-Cola bought the brand in 2007. The G-Unit line of clothing and the G-Unit record label that he started with his manager Sha Money XL in 2003 also bolsters his bottom line. A signature scent is reportedly in the works.

Beyonce Knowles is second. Famous thanks to her vocal chops, her distinct style and strong presence has allowed her to translate her fame into the fashion and film arenas, as well.

• In pictures: Secrets Of Celebrity Health
• In pictures: The Gatekeepers

As an actress, she was in the holiday sensation Dreamgirls, which earned $154 million worldwide. Her label House of Dereon, which had a slow start, had wholesale sales over $10 million last year.

Another remarkable young mogul musician is Justin Timberlake. Timberlake's FutureSex/LoveShow tour grossed $127 million in 2007 and reached millions of living rooms with an HBO special. Non-musical ventures include the William Rast clothing line, the BBQ restaurant Southern Hospitality in New York City and record label Tennman Records.

In an attempt to identify these moguls in the making, we took a look at Hollywood's top earners under age 35 with significant income from more than one industry with the potential to grow as celebrity powerhouses deep into the century.

Aside from talent, they have other things in common. Almost all the members on our list have a perfume line and/or a fashion endeavor on their resume. While perfume is a relatively painless and fruitful way to build a celebrity's brand, fashion is a complicated and fickle business.

A clothing brand must introduce new collections for every season, has to fight for retail floor space and operates with relatively limited advertising. The runways are littered with the ghosts of lines that have petered out--Eve's Fetish line, Sean Comb's line for women, and, though through no fault of the stars, the various celebrity lines attached to Steve & Barry's.

Two stars that have weathered the fashion industry's furor are Mary Kate and Ashley Olsen. They were the first young stars to tap into the retail power of young girls with their licensed line in Wal-Mart that ended earlier this year after nine years on the shelves. The actresses have now parlayed their fame and talents into creating adult fashion lines--and celebutante favorites--The Row and Elizabeth and James.

Of course, the celebrity marketing and branding machine that seeps into nearly all corners of retail is mutually beneficial. The celebrities boost their earnings and capitalize on their fan base while the retailers end up with an exclusive product. "It ties into consumer aspirations," says Stone.

That's not all. In order to strengthen a celebrity's brand, business ventures and licensing deals must match the star's personal attributes, beliefs and style. "It's got to be more than commerce," says Bragman. "It's got to be believable."

• In pictures: China's 25 Most Powerful Celebrities