Valve founder Gabe Newell has a net worth around $5.5 billion, according to the most recent rich list put together by business magazine Forbes. If correct, that would mean his personal worth has grown by $1.4 billion since the same outlet estimated Newell to be worth $4.1 billion in January of this year.

Newell is said to own around half of Valve, the company behind the Steam platform and developer of series such as Half-Life, Portal, and Counter-Strike. He is placed joint-97th on Forbes' list of the 400 wealthiest people in America, putting him ahead of Uber founder Travis Kalanick (115th), Star Wars creator George Lucas (118th), and legendary film director Steven Spielberg (206th) and behind media giant Rupert Murdoch (39th) and Tesla CEO Elon Musk (21st).

Microsoft founder Bill Gates tops the list this year with a net worth of $89 billion, ahead of America's second-richest person, Amazon founder Jeff Bezos ($81.5 billion). Facebook CEO Mark Zuckerberg lies fourth with a fortune of around $71 billion.

Unlike Activision, EA, Take-Two, Ubisoft, Nintendo, Sony, and Microsoft, Valve is not a publicly traded company. That's part of the reason why we don't officially know Valve's net worth. Some publicly traded companies also disclose their executives' salaries, but Valve doesn't do this since it's private. In other Valve-related news, Steam users can currently try Warhammer 40,000: Dawn of War III and Warhammer: End Times - Vermintide for free.