By Simon Atkinson
Business Reporter, BBC News
He doesn't bother with private jets, shuns flashy offices, and for most of the 1990s made do with a plastic watch.
Critics feel Mr Slim should have given away more of his wealth
And while he does have a laptop, he is adamant that he does not use it, saying: "I'm a paper man, not electronic."
Not the kind of attributes you might expect from someone who, according to reports, has overtaken Bill Gates to become the world's richest man.
Mexican tycoon Carlos Slim is now worth $67.8bn (£33.6bn), as against the Microsoft founder's $59.2bn, financial website Sentido Comun says.
Latest figures from US magazine Forbes, known for its rankings of the world's wealthiest, show 67-year-old Mr Slim at number two, ahead of US investor Warren Buffett but behind Mr Gates, although these were compiled in April.
His surging fortune appears to have been helped by 27% growth in the value of shares in America Movil, Latin America's largest mobile phone company, in which Mr Slim holds a 33% stake.
Mr Slim, whose heavy-set figure belies his name, also owns the Inbursa financial group and the Grupo Carso industrial conglomerate, whose interests range from retail stores to restaurants.
Meanwhile, the infrastructure firm he owns, Ideal, is working on a project to develop a shopping centre, schools and a hospital in Mexico City.
The baseball-mad engineering graduate made enough money from working in property early in his career to invest in the stock market.
During the Latin American economic crisis of the early 1980s, Mr Slim made a name for himself - and substantial profits - by buying a number of struggling companies at very low prices before transforming their fortunes.
And in 1990, he oversaw the privatisation and overhaul of Telefonos de Mexico (Telemex) - the state telephone company.
Like Mr Buffett, Mr Slim has done some canny deals in the stock market - not least, buying shares in Apple when they were $17 dollars each. They are now worth well over $100.
The son of Lebanese immigrants, he has set his three sons up in business and is known for his philanthropy - though not on the scale of Mr Gates or Mr Buffett.
Most recently, he linked up with former US president Bill Clinton and Canadian mining figure Frank Giustra to launch an anti-poverty campaign in Latin America, and in March pledged $6bn for his three charitable foundations.
In Mexico where, according to World Bank data, about 50% of people are living in poverty, many feel that he has not donated enough, especially given how ubiquitous his companies are in day-to-day life.
However his supporters say that some of that criticism is unfair, not least because of his relatively recent elevation to the ranks of the mega-rich.
And Mr Slim, has said he is not convinced that philanthropy is the best way to help people.
"(Bill) Gates has to study how he can (fight poverty) in the same way that Microsoft...succeeded in business, because charity has not solved the problem," he told USA today.
"It's based on my conviction that poverty is not fought with donations, charity or even public spending, but that you fight it with health, education and jobs."
Still working, the tycoon has indicated he has no desire to retire from business to concentrate more on charitable work, as Mr Gates has done.
As he said in a recent interview: "Wealth is like an orchard. You have to share the fruit, not the trees."