Gates back on top of Forbes' billionaire rankings

The largest net worth gainer on the list was Facebook's Mark Zuckerberg, who more than doubled his fortune to $28.5 billion as the value of his company's stock soared. He ranks 21st on the list.

The social media giant helped bring a few notable newcomers to the list, including Facebook's Chief Operating Officer Sheryl Sandberg and WhatsApp founders Jan Koum and Brian Acton, who recently sold their business to Facebook for $19 billion.

Forbes said 268 billionaires were new to the list, beating out a prior high of 226 newcomers in 2008. And a record number of women made the list this year, with 172 women joining, up 25 percent from last year.

Altogether 100 people dropped out of the rankings, while 16 passed away.

The U.S. was the country with the greatest number of billionaires at 492, followed by China with 152 and Russia with 111. Billionaires from four new countries joined, adding Algeria, Lithuania, Tanzania and Uganda to the geographic mix.