Gabe Newell, who owns more than half of Valve, is estimated to have a net worth of $1.5 billion dollars, making him the 854th richest billionaire in the world, reports Forbes.

The Valve co-founder and managing director makes his debut on the Forbes rich list after a hugely successful year for Valve in 2011, thanks to more than 40 million Steam users and strong sales of Portal 2.

Valve doesn't share very much about revenues so Newell's personal worth has been estimated by Forbes after consulting with video game industry insiders, equity analysts, investment bankers, and technology analysts. The most conservative estimates put Valve's value at more than $3 billion, and with his hands in more than half of that pie, Newell is worth at least $1.5 billion.

Newell co-founded Valve back in 1996 after cashing in stock options earned during his time at Microsoft.

Forbe's list of The World's Billionaires features an all-time high 1,226 billionaires worth a record $4.6 trillion. It includes 128 new billionaires, from 32 countries.

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