This year it took at least US$3.7bil (RM16.3bil) in wealth to make it onto the list, but only in a tie for 501th place, a group that included Hollywood director Steven Spielberg.
US President Donald Trump came in at No.544 on the list, with a net worth estimated by Forbes of $3.5 billion - double that of Thaksin and behind Thailand's four richest men.
Gates' $86 billion in wealth tops 2,043 other billionaires - a number that jumped 13 percent from 1,810 a year ago.
Forbes said that much of the decline in Trump's net worth is due to softness in the midtown Manhattan real estate market.
"Although Donald Trump's name is plastered on buildings all around the world, his core assets are still located in a small part of New York City", said Dan Alexander, an associate editor at Forbes Media. "Lately, the neighbourhood has been struggling (relatively speaking)", Forbes said.
President Donald Trump met with Microsoft Corp.co-founder Bill Gates at the White House on Monday, just days after releasing a budget proposal that would impose deep cuts on funding for numerous causes championed by the billionaire philanthropist.
"When I first got involved in health and development more than 15 years ago, the main motivation was to save and improve people's lives around the world".
The US had the most billionaires with 565, while China was second with 319, and Germany was in the third spot with 114.
Forbes has just released its latest report on the world's billionaires and it might surprise you to know that 12 Malaysians have made it on that exclusive list.
Mr Trump also spent millions of dollars on his campaign, which he claims to have self-funded, though this is fiercely disputed. That would be Bill Gates, who is worth $86 billion.
The Trump administration asked for a 28.5 percent cut in global programs, including the State Department and the U.S. Agency for worldwide Development, for the year that begins October 1. versus fiscal 2016, the last year Congress enacted full-year spending legislation.
Amancio Ortega: Ortega co-founded the hugely successful high street Spanish retail chain Zara, and now boasts a net worth of $74 billion.
As the New York's real estate market has slowed, Forbes began downgrading Trump's net value previous year, saying in October that his net worth was down to US$3.7b. The youngest member of the list is John Collison, the 26-year-old founder of Internet payment startup Stripe, who boasts a net worth of $1.1 billion.
HollywoodLifers, are you surprised Trump plummeted down so low on the list?