Microsoft's Bill Gates overtakes Mexico's Carlos Slim as world's richest person

The surging price of Microsoft shares returned US tech tycoon Bill Gates back to the top of Forbes's world's billionaires list, with his $76 billion beating out Mexico's Carlos Slim's $72 billion.

The annual list, released Monday, counted 1,645 men and women as billionaires, with an average wealth of $4.5 billion and a collective wealth of $6.4 trillion, up $1 trillion from a year ago.

Gates, co-founder of the US software firm, showed his staying power at the top -- the world's richest man for 15 of the past 20 years, according to Forbes -- despite spending recent years giving away large sums of money to global health and anti-poverty programs.

Gates owns about 4.4 percent of Microsoft, making up less than 20 percent of his total fortune.

But the company's share price has risen 25 percent over the past year, and, along with gains in other assets, he has added $7 billion to his fortune since a year ago, according to Forbes.

Slim, with a hand in everything from telecommunications (America Movil) to mining, finance and industry (Grupo Carso), to retailing and real estate across the Americas region, was worth $1 billion less than a year ago, hit in part by sagging markets in South America.

In third was Spain's Amancio Ortega, whose pockets have filled with profits from fashion: his hugely successful Inditex garment empire, parent of popular chains Zara, Pull & Bear, and Bershka. More recently, Ortega heavily invested in real estate in Europe and the United States; his worth was put at $64 billion.

A familiar cast of mega-wealthy filled out the rest of the top ten: US investment guru Warren Buffett ($58.2 billion); software group Oracle's founder and chief executive Larry Ellison ($48 billion); US industrialists and brothers Charles and David Koch (each with $40 billion); Las Vegas casino king Sheldon Adelson ($38 billion); Walmart heiress Christy Walton ($36.7 billion) and her brother Jim Walton ($34.7 billion).

Together the $507 billion held by the top ten is larger than the entire size of the economy of Norway, or Belgium or Poland in 2012.