Slim, a telecommunication magnate tops the list for the fourth year in a row with a net worth of $73 billion.
Bill Gates held on to second place at $67 billion.
Spanish clothier Amancio Ortega moved into the top three with a net worth of $57 billion, pushing Warren Buffett to No. 4. It's the first time Buffett has been out of the top three since 2000.
A record 1,426 people made Forbes' latest annual tally of billionaires, up 16 percent from last year.