Here is the list of the richest billionaires in the world, their net worth and what they do. This list is according to Forbes rating for the year 2015.

BILL GATES: net worth - $79.2 billion. Age , 59.  He is an American business magnate, philanthropist, investor, and computer programmer. He is the  co- founder Microsoft which is the largest PC software company in the world. Gates held the positions of chairman, CEO and chief software architect, and was the largest individual shareholder until May 2014. Gates has authored and co-authored several books. He is considered one of the best entrepreneurs in the world and has held the post of the richest person in the world for 16 times out of 21 years.
CARLOS SLIM: net worth - $77.1 billion. Age, 75.  is a Mexican business magnate, investor, and philanthropist. Slim is the chairman and chief executive of telecommunications companies Telmex and América Móvil, Latin America's largest mobile-phone carrier. Slim's total conglomerate comprises a diverse portfolio of businesses from a wide array of industries that include telecommunications, education, health care, industrial manufacturing, food and beverages, real estate, airlines, media, mining, oil, hospitality, entertainment, technology, retail, sports and financial services.

WARREN BUFFETT: net worth - $72.7 billion. ) age, 84   is an  American businessman, investor and philanthropist. He is the most successful investor in the world. He is the chairman, CEO and largest shareholder of Berkshire Hathaway. He is also active in contributing to political causes, having endorsed  Democratic candidate Hillary Clinton for president during the 2016 campaign season.
AMANCIO ORTEGA: net worth - $64.5 billion. Age, 78 he is a Spanish fashion businessman and founding chairman of the Inditex fashion group, best known for its chain of Zara clothing and accessories retail shops.

LARRY ELLISON: net worth - $54.3 billion age, 70 he is an American internet entrepreneur, businessman and philanthropist. He serves as executive chairman and chief technology officer of Oracle Corporation

CHARLES KOCH: net worth - $42.9 billion age 79 is an American businessman and philanthropist. He is co-owner, chairman of the board, and chief executive officer of Koch Industries. He and his brother inherited the business from their father, Fred C. Koch, and then expanded the business. Originally involved exclusively in oil refining and chemicals, Koch Industries now includes process and pollution control equipment and technologies; polymers and fibers; minerals; fertilizers; commodity trading and services; forest and consumer products; and ranching.
DAVID H KOCH: net worth - $42.9 billion age 74 is an American businessman, philanthropist, political activist, and chemical engineer. He joined the family business Koch Industries, a conglomerate that is the second-largest privately held company in the United States, in 1970. He became president of the subsidiary Koch Engineering in 1979, and became a co-owner of Koch Industries, with older brother Charles, in 1983. He is now an executive vice president.

CHRISTY WALTON & FAMILY: net worth - $41.7 billion age, 60 is the widow of John, one of the sons of Sam Walton, the founder of Wal-Mart. She is the world's leading female philanthropist   according to the amount she gives as a percentage of her wealth.
In June 2005, she inherited her husband's fortune of US$18.2 billion following his death in a plane crash. As of 2015 Walton is the richest woman in the world. According to Forbes, she is the 6th richest person in the United States, and the 8th richest person in the world, as of March 2015. Forbes reported that she was the richest woman in the world for eight years running, and still held the title in March 2015. As of March 2014, she and her family (not including her two brothers-in-law and a sister-in-law) had an estimated net worth of $36.7 billion,  the bulk of which comes from her shares in Wal-Mart, but also from First Solar, in which her husband invested.

JIM WALTON: net worth - $40.6 billion age, 66  , he  is the third child of Wal-Mart co-founder Sam Walton and Helen Walton  with siblings Rob Walton, Alice Walton, In 1972, he joined Wal-Mart and was involved in its real estate dealings. After serving for four years he moved to the family owned Walton Enterprises as president in 1975
LILIANE BETTENCOURT & FAMILY: net worth - $40.1 billion age 92  is a French heiress, socialite, businesswoman and philanthropist. She is one of the principal shareholders of L'Oréal one of the world's largest cosmetics and beauty companies.