Gabe Newell co-founded Valve in 1996. His first game at the studio, Half-Life, was critically acclaimed

Video game entrepreneurs Markus Persson and Gabe Newell have both joined an annual list which estimates who are the world’s richest people.

Newell, who co-founded Valve in 1996, has cultivated the company during its pioneering transition to the digital PC games business. Its flagship platform, Steam, has amassed more than 125 million active users since its launch in 2003. With Newell the majority shareholder at Valve, his net worth is currently $1.3 billion.

According to Forbes, which estimates his net worth, Newell is one of the 500 richest people in the US.

Joining him on the list is Markus Persson, better known by his online handle “Notch”, whose net worth is also put at $1.3 billion.

Persson is one of the youngest entrepreneurs to join the list. He founded the Sweden studio Mojang in 2009, when his breakthrough game Minecraft escalated into a phenomenon.

In November, Microsoft announced it was buying Mojang for $2.5 billion. Persson, who owned 70 percent of the company, stood to make $1.75 from the deal.

The full 2015 Forbes Rich List puts Microsoft co-founder Bill Gates at the top, with an estimated net value of $79.2 billion.