New York: Microsoft co-founder Bill Gates has retained his position as the richest person in America for the 19th year in a row this year, according to Forbes’ annual ranking of the nation’s 400 super rich people who have a combined net worth of $ 1.7 trillion dollars.

With a net worth of $ 66 billion, Gates not only remained the richest person in America but is also “the planet’s most generous person”, thanks to his countless philanthropic endeavours in developing nations, including India, Forbes said.

The 56-year old Harvard dropout has given away $ 28 billion to philanthropic causes so far, with his new obsession being building better toilets for those without water or sewage systems, it added.

Every year 1.5 million children die from food and water tainted with fecal matter, more than the annual deaths from AIDS and malaria combined, Forbes said.

The Bill and Melinda Gates Foundation is also spearheading a malaria vaccine that is showing promise in clinical trials. The non-profit Global Alliance for Vaccines and Immunisation (GAVI) founded by Gates has raised $ 4.3 billion in pledges from various countries to provide life-saving vaccines against a range of deadly infections.

“Gates and his good friend Warren Buffett continue to recruit new members to their Giving Pledge, in which the very wealthy promise to give away at least half of their net worth during their lifetime or after they die,” Forbes said.

Gates’s net worth rose $ 7 billion since last August on the back of Microsoft shares, which climbed 20 per cent and on gains from investments in private equity, bonds and stocks, Forbes said.

In addition, Gates continues to sell shares of Microsoft and now just one-fifth of his net worth stems from the software company he co-founded 37 years ago.

On the second spot with a $ 46 billion networth is 82-year-old Buffett, chairman of Berkshire Hathaway, who recently completed radiation treatment for prostate cancer.

Earlier this year, Buffett said he had picked his CEO replacement but has declined to give a name.

Among the names of possible successors making the rounds is Berkshire’s head of reinsurance business India-born Ajit Jain.

Buffett is not too far behind Gates when it comes to philanthropy. He gave $ 1.5 billion to the Gates Foundation in July, bringing his total contribution to $ 17.25 billion.

On his birthday in August he pledged $ 3 billion Of stock to his children’s foundations. His fortune grew $ 7 billion as class A shares jumped more than 20 per cent since last year.

Forbes said the combined net worth of the 2012 class of the 400 richest Americans is $ 1.7 trillion, up 13 per cent from the $ 1.5 trillion a year ago.

The average net worth of a Forbes 400 member is a staggering $ 4.2 billion, up from $ 3.8 billion dollars and the highest ever, as two-thirds of the individuals added to their fortunes in the past year.

“The gap between the very rich and the merely rich is widening. Only two in the top 20 are poorer, and as a group they are worth $ 73 billion more than a year ago,” it said.

On the third spot is Oracle head Larry Ellison, whose net worth grew $ 8 billion to $ 41 billion, the biggest dollar gain of anyone on the list this year.

The country’s three richest entrepreneurs drove much of those gains, continuing to add billions to their net worth, even as they give money away, Forbes said.

While winners outnumbered losers by nearly four to one, there were some stunning drops.

“No one fell more dramatically than Facebook s Mark Zuckerberg,” whose fortune stumbled $ 8.1 billion, making him the year’s biggest loser.

Zuckerberg ranked 36th on the list with a net worth of $ 9.4 billion but he is still $ 2.5 billion richer than he was two years ago and he’s “handily entrenched in the ranks,” Forbes said.

“Zuckerberg has faced a rough road since Facebook went public in May. The stock of the social networking company has performed poorly, falling below $20 in August after debuting at $38.”

In July the company reported a net loss of $ 157 million for its second quarter, driving the stock price down.

“What is less clear is whether the young executive, who married his longtime girlfriend Priscilla Chan the day after the IPO and headed off for an Italian honeymoon, can right the ship and make Facebook into a winning public company,” the publication said.

Newcomers to the exclusive club of 400 include widow of Apple co-founder Steve Jobs, Laurene Powell Jobs who is now the wealthiest woman in Silicon Valley, and Twitter co-founder Jack Dorsey. Jobs was placed 28th on the list with a net worth of $ 11 billion.

Just 45 women made it to the list, up from 42 last year, Forbes said.

Others on the list are New York Mayor Michael Bloomberg at rank 10, Amazon.com founder Jeff Bezos (11), Google co-founders Sergey Brin and Larry Page (13), media titan Rupert Murdoch (36), business tycoon Donald Trump (128), talk show host Oprah Winfrey (151) and Starbucks Chairman Howard Schultz (311).

The Forbes ranking of the nation s super rich was launched in 1982 when a net worth of 75 million dollars assured one of a place in the list.

This year’s entry fee is $ 1.1 billion dollars. There were just 13 billionaires when the list was launched and the total worth of the 400 club was a mere $ 93 billion.