Mexican tycoon Carlos Slim may be the world's richest man but he limits his monthly salary to $24,000 and travels in a Suburban, according to his latest biography.
Mr Slim, 70, knocked Bill Gates from the top of the Forbes list of the world's billionaires this year with an estimated fortune of $53.5 billion.
He began his business career aged 10, selling sweets and drinks to his family and later made his name with aggressive investments during crises.
"Unlike aristocrats, the jet set or the monarchy, he's extremely simple," biographer José Martinez said as a new edition of his 2002 book, Carlos Slim, Unpublished Portrait, was set for release across Latin America.
According to his biographer, Mr Slim's fortune far exceeds the amount calculated by Forbes.
The fifth of six children - three boys and three girls - Mr Slim was born into a well-off family, including a Lebanese immigrant father, in Mexico City in January 1940.
Mr Slim studied civil engineering and later built up the telephone monopoly Telmex after acquiring it from the government in 1990.
He hit the top spot of billionaires after his fortune rose $18.5 billion in 12 months, and shares of America Movil, of which he owns a $23 billion stake, were up 35 per cent in a year, according to Forbes.
Last year he injected $250 million into the ailing New York Times, becoming its second biggest partner and surprising some in the media.
"He has no say nor vote. He did it to support the paper in a crisis and he intends to sell it, but the group hasn't yet recovered," Mr Martinez said.
The soft-spoken billionaire's empire is ever-present in Mexico, including department stores, construction companies and the Inbursa financial group.
He has invested more than $60 billion in Latin America in the past 10 years.
"All this was done by a man who fixes his salary at $24,000 a month and at the same time controls between 30 and 40 per cent of the Mexican stock exchange," his biographer said, adding that until recently Mr Slim wore a plastic watch.
Mr Slim repeats the maxim "never do business with politicians". He "lives a frugal life which borders more on modesty than sobriety," Mr Martinez wrote in the biography.
Austerity rules in his business empire's offices, he added.
"The highest and middle executives share the same secretary, and there are no advisers."
One of Mr Slim's daughters, however, manages his private art collection which is the largest in Latin America and includes some 300 works by French sculptor Auguste Rodin.
"I would say I am restrained, and my children are too, out of taste and conviction, not out of discipline," Mr Slim has said.