The U.K.-based newspaper reports that the American family has a collective net worth of £128.9 billion (nearly $175 billion) in its 30th annual list published on Sunday, May 13. Brothers Charles and David Koch, worth £88.9 billion ($120 billion), place second.
Although Amazon CEO and founder Jeff Bezos comes in third, he's still the world's single richest person with a net worth of £83 billion ($112 billion). Two other individuals round out the top five: Microsoft co-founder Bill Gates, worth £66.7 billion ($90 billion) and Berkshire Hathaway CEO Warren Buffett, worth £62.2 billion ($84 billion).
While Bezos may be the world's richest man, Walmart heiress and philanthropist Alice Walton remains the world's richest woman, according to the Forbes 2018 billionaires list. The youngest of Sam Walton's children, Alice Walton, 68, is reportedly worth $40.5 billion.
Her elaborate $500 million art collection and donation of $225 million in Walmart shares to the Walton Family Foundation in 2016 were two major components of raising the family's overall wealth, the Sunday Times reports.
"My parents spent a lot of time with us growing up talking about the importance of giving back," Alice Walton said in a 2011 CBS News interview.
The Walton Family also reaps the benefits from other Walmart-owned companies, such as the warehouse chain Sam's Club and the British supermarket chain Asda. Walmart, as the no. 1 Fortune 500 company, has become a lot larger than its late founder Sam Walton first envisioned.
While getting his degree in economics at the University of Missouri at Columbia in the 1930s, Walton waited tables, delivered newspapers and clerked at a five-and-dime.
He opened the first Walmart store in Arkansas in 1962 and built his retail business on the premise that Walmart should service rural areas and "help customers, cut costs and share profits."
His company grew rapidly and went public in 1970. Sales associates who had remained with the company and received Walmart shares saw their own wealth grow, CNBC anchor David Faber reports in the documentary "The Age of Walmart."
Walton and his wife Helen raised four children, Rob, John, Jim, and Alice. In 1992, President George H. W. Bush awarded Walton the Presidential Medal of Freedom. The Walmart founder passed away the same year. By then, his family was already the richest in the nation, and his New York Times obituary called him "the most successful merchant of his time."
"My parents didn't believe value and worth had anything to do with money. I think it's always been important to keep your feet on the ground and your nose out of the air," Alice Walton told CBS News.
Though her wealth helped increase the family's bottom line, the billionaire still holds tight to one of her father's frugal habits: driving an old, cheap car. Sam Walton drove around the 1979 version of the same truck until he died over a decade later, and other members of the Sunday Times Rich List, including Bezos, Buffett and Mark Zuckerberg, also have a habit of driving old cars.
The world's richest woman's vehicle of choice is a 2006 Ford F-150 King Ranch, which has a modest price of around $40,000.
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