Donald Trump may be the Republican front runner for the White House, but he is slipping behind in the world billionaires race, Forbes magazine's new list of the planet's richest people shows.

Mr Trump, who has made his enormous wealth a key selling point in his presidential bid, came in 324th in the magazine's 2016 ranking of the world's billionaires.

That means that more than 200 billionaires have jumped ahead of the ever-competitive real-estate mogul since 2015 when he placed 121st on the annual list.

The magazine put Trump's net worth at an above-average $4.5bn (€4.1bn), the same as last year but about half the $10bn (€9.2bn) fortune candidate Mr Trump often claims to have amassed.

Six Irish citizens are members of the billionaires’ club with a combined net worth of more than $30bn (€27.6bn).

Businessman Denis O’Brien is valued at $5.7bn (€5.2bn) and is 219th; Financier Dermot Desmond is estimated as being worth $1.9bn (€1.7bn); Glen Dimplex founder Martin Naughton has $1.6bn (€1.5bn); Campbell’s soup heir John Dorrance is worth $2.7bn (€2.5bn); Indian construction businessman Palloni Mistry is worth $12.5bn (€11.5bn) and has Irish citizenship; and US Lone Star Funds owner John Grayken also has Irish citizenship and is worth $6.3bn (€5.8bn). 

In other highlights, Microsoft co-founder Bill Gates is still ranked the world's richest person with an estimated net worth of $75bn (€69bn), $4.2bn (€3.9bn) less than last year.

Facebook chief executive Mark Zuckerberg had the best year of all, adding $11.2bn (€10.3bn) to his fortune.
Forbes put the 31-year-old's net worth at $44.6 bn (€41bn), ranking him number six, just behind Amazon's Jeff Bezos at $45.2bn (€41.6). It was the first time either of them made the top ten.

It has not been a banner year for billionaires, however. 

According to Forbes, their number has slipped to 1,810, 16 fewer than last year and their aggregate net worth shrank by $570bn (€524bn) to $6.48 trillion (€6 trillion).

This is also the first year since 2010 that the average individual billionaire's fortune has dropped, settling at $3.6bn (€3.3bn), $300m (€276m) less than last year, it said.

Volatile stock market

A volatile stock market, cratering oil prices and the strong dollar have reshuffled the ranks of billionaires, the magazine said.

Only two held on to their previous year's rank - Mr Gates, who has been number one for three straight years, and investor Warren Buffet, whose $60.8bn (€56m) fortune put him in third place.

Mexico's telecoms magnate Carlos Slim slipped to fourth place, giving up second to retailer Amancio Ortega of Spain $67bn (€61.6bn). Slim's fortune plunged from $77.1bn (€71) to $50bn (€46bn).

Forbes said 221 people fell off the list altogether, replaced by 198 newcomers.

The youngest billionaire was 19-year-old Danish heiress Alexandra Andresen. Her 20-year-old sister Katharina is the second youngest on the list.

In all, 66 billionaires are under 40 years of age. The richest of the 190 women on the list was Liliane Bettencourt of France who was ranked 11th with $36.1 billion (€33.2bn), down from $40.1bn (€36.9bn) last year.

The United States is still the country with the most billionaires (540), followed by mainland China (251) and Germany (120).

Russia has 77 billionaires, Hong Kong 69, and Brazil 23, down from 31 last year.