1. Bill Gates
Net Worth $81B
Source of Wealth: Microsoft, self-made

America’s richest man, Bill Gates, is using his billions to effect major social change around the globe. The Bill & Melinda Gates Foundation has given away $30 billion since 2000, a fortune that on its own would be the 16th largest in America. Smallpox has disappeared, polio is nearly gone too, and the American education system has gotten an overhaul. Gates is not the only one responsible for the changes, but none of them would have happened without the help of the biggest philanthropist in world history. Now he’s taking on the deadliest animal on Earth, the mosquito.
Bill Gates
Malaria cases are down 25% since 2000, but there are still 200 million cases worldwide, and Gates is throwing billions toward making that number zero. He’s also taking sight at second deadliest animal on Earth, humans. Along with Microsoft cofounder Paul Allen, Gates is funding a Washington state-based group fighting for universal background checks on guns. Meanwhile, Gates keeps getting richer, adding $9 billion to his net worth in the last year.

The gain is partly due to a sharp rise in shares at Microsoft, where Gates stepped down as chairman to take a different role advising current management on new products and technologies. His fortune is also up thanks to big returns on his investments in Canadian National Railway and trash company Republic Services, which Gates holds through his investment firm Cascade. He also owns chunks of tractor maker Deere & Co. and South American McDonald’s franchise Arcos Dorados (“golden arches” in Spanish).

2. Warren Buffett
Net Worth: $67B
Source of wealth: Berkshire Hathaway, self-made

Warren Buffett‘s net worth continues to surge, despite his giving away billions, thanks to the juggernaut performance of Berkshire Hathaway. The company’s coveted Class A stock, which is the most expensive of any public U.S. company, eclipsed $200,000 per share for the first time in August, lifting Buffett’s net worth by $8.5 billion over the past year. With dozens of subsidiaries, including in railroads, insurance and energy, Berkshire Hathaway posted $182 billion in 2013 revenue and $19.5 billion in net income.

Known as the Oracle of Omaha, his company is Coca-Cola‘s largest shareholder. Buffett took heat from some critics in April after he called Coca-Cola’s employee compensation plan excessive, yet declined to vote against it. He bested his own giving record in July, giving away Berkshire shares worth $2.8 billion, primarily to the Gates Foundation but also to his children’s foundations, bringing his lifetime giving total to nearly $23 billion.

He told his shareholders this year that his best ever investment was buying Benjamin Graham’s book “The Intelligent Investor” in 1949. He later studied under Graham before moving home to Nebraska and acquiring a struggling textiles company in 1962. That company is still called Berkshire Hathaway, but it’s now the fourth most valuable public company in the U.S. with a market capitalization in early September of $330 billion

3. Larry Ellison
Net Worth: $50B
Source of Wealth: Oracle, self-made

Larry Ellison shocked the business world this September when he announced plans to step down as Oracle’s CEO. After having built databases for the CIA, Ellison founded Oracle in 1977 and has never left. He will remain Chief Technology Officer. An adrenaline junkie, he was arguably the first Silicon Valley hotshot to live large and very, very fast. After having suffered intense mountain biking and bodysurfing accidents, Ellison turned to sailing, where he’s the main backer of America’s Cup winner Oracle Team USA.

In recent years, he’s been buying up properties on the Hawaiian island of Lanai, which he bought for a reported $300 million in 2012. He is said to own every hotel room on the island. His daughter Megan Ellison has found success as a film producer, having founded Annapurna Pictures, which was behind hits like Zero Dark Thirty and American Hustle. Ellison never met his biological father and was raised in a middle-class Chicago home by his great-aunt.

4. Charles Koch
Net Worth: $42B
Source of Wealth: diversified, inherited and growing

Lightning rod-capitalists Charles and his brother David have added to their already substantial empire, plunking down more than $5 billion on acquisitions in the past year. New additions like inkmaker Flint Group and PetroLogistics go well with what the Kochs already have. Charles has been chairman of Koch Industries since 1967, overseeing massive growth of the now second biggest private company in America, which owns oil pipelines, refineries and manufacturers of building materials, paper towels and even Dixie Cups.
The Kochs are concerned not only with profits but with politics, too. They’ve opened up their big checkbooks in an effort to help Republicans retake the senate. The Kochs, say Sen. Harry Reid (a Democrat), are “actually trying buy the country.” But then they go ahead and do something that confounds critics. Like baking Libre, a fast-growing group aimed at gaining Latino support for limited government, or giving $25 million to the United Negro College Fund.

4. David Koch
Net Worth: $42B
Source of Wealth: diversified, inherited and growing

New York City’s richest resident, David Koch shares control of America’s second largest private company, $115 billion (sales) Koch Industries, with his older brother Charles. The brothers have added to their already substantial empire, plunking down more than $5 billion on acquisitions in the past year. New additions like inkmaker Flint Group and PetroLogistics go well with what the Kochs already have.

The Metropolitan Museum of Art in New York dedicated the David H. Koch Plaza in September, part of a $65 million renovation he funded. David also has given more than $100,000 to Republicans for the 2014 midterm elections, while Koch Industries has poured more than $3 million into the midterm campaign, prompting Sen. Harry Reid to accuse them in January of “actually trying to buy the country.” A Koch spokesman said Reid’s comment was “disrespectful and beneath the office he holds.” Audio recordings leaked from not-so-secret Koch-organized meetings in June revealed Republicans including Sen. Mitch McConnell (R-Ky.) laying out their strategy for thwarting Obama’s legislative agenda should they gain control of the Senate this year.

5. Christy Walton
Net Worth: $38B
Source of Wealth: Wal-Mart, inherited

Christy Walton is the wealthiest woman not only in the U.S., but also in the world, more than $1 billion wealthier than L’Oreal heiress Liliane Bettencourt. In the U.S., the next richest is her sister-in-law Alice Walton, who trailed by $3 billion as of mid-September 2014. Christy married into what is now the richest family in the world (worth more than $150 billion) and inherited her wealth when husband John Walton, a former Green Beret and Vietnam war medic, died in an airplane crash in 2005. She’s the wealthiest of the Waltons thanks to a side investment by John that turned into a major score: solar energy company First Solar. Her nearly 27% stake is worth some $1.8 billion.

The bulk of her holdings are in Wal-Mart, the massive retailer founded by her father-in-law Sam Walton and his brother James in 1962. She will receive $470 million in Wal-Mart dividends after taxes in 2014. Walton leads a very private life in Jackson, Wyoming, but last year had a rare bit of publicity when she was given an award by the Imagen Foundation for producing the film “Bless Me, Ultima,” based on the book by Rudolfo Anaya, who is considered the father of Chicano literature. Her son battled cancer when he was just three years old and she fought a case of pneumonia that nearly killed her, according to the Imagen Foundation.