KATHMANDU, March 3: The Microsoft founder once again beat Mexican businessman Carlos Slim to the top spot.
Mr Gates’ net worth rose by just over $3bn (£1.94bn) in the year to 13 February, to $79bn.
There are a record 1,826 billionaires in the world, Forbes said, an increase of 181 in the past 12 months.
Mr Gates has now been top of the list for 16 of the last 21 years, Forbes added.
Legendary US investor Warren Buffett regained third place in the list with a net worth of $72.7bn, from Amancio Ortega, the founder of Spanish fashion chain Zara.
Forbes 2015 ranking of richest people:
1. Bill Gates $79.2bn (Microsoft)
2. Carlos Slim Helu $77.1bn (Phones and construction in Mexico)
3. Warren Buffett $72.7bn (Global investor)
4. Amancio Ortega $64.5bn (Zara and other fashion chains)
5. Larry Ellison $54.3bn (Oracle data storage technology)
6. Charles Koch $42.9bn (Industrialist)
7. David Koch $42.9bn (Industrialist)
8. Christy Walton $41.7bn (Walmart retail giant)
9. Jim Walton $40.6bn (Walmart retail giant)
10. Liliane Bettencourt $40.1bn (L’Oreal cosmetics firm)
Facebook’s Mark Zuckerberg makes the Forbes top 20 rich list
The funds required to make it into the top 20 in the list have fallen by $2bn to $29bn this year.
The founders and chief executives of US technology firms dominated the list again, accounting for six of the top 20 richest men in the world.
The first woman on the rich list is Christy Walton, the widow of John Walton, one of the heirs to the Wal-Mart retail empire.
She has been declared the richest woman in the world for five of the last six years by Forbes.
Facebook’s Mark Zuckerberg moves up five places in the rankings to number 16, with a net worth of $33.4bn. This is the first time he has been included in the list of the world’s 20 richest people.
The youngest billionaire in the world is 24 year-old Evan Spiegel, the co-founder of messaging app Snapchat, with a fortune of $1.5bn.
Silicon Valley has produced 23 new billionaires this year including co-founders of car-hailing service Uber, Travis Kalanick and Garrett Camp, and their first employee, Ryan Graves.
Elizabeth Holmes, the founder of blood-testing firm Theranos, has debuted on the global list as the youngest self-made woman at age 31, with a fortune of $4.5bn.
Elizabeth Holmes is the youngest self-made woman on the Forbes list
The US also dominates the top 20 with 15 of the world’s richest people coming from America.
This list includes 290 newcomers, 71 of whom come from China. There is also a new record of 46 billionaires under under the age of 40.
One hundred and thirty-eight people from last year’s list dropped out of the ranks altogether. Most notable of these is current Ukrainian President and former “chocolate king” Petro Poroshenko.
Meanwhile, Guatemala has a billionaire for the first time in Mario Lopez Estrada, who owns Comcel, which has about half of the mobile phone market in the country. He ranks as 1741 on the list.