Guitar Hero III is the first video game to generate over $1bn in sales

"Speaking during a CES keynote in Las Vegas on Friday, Activision Publishing CEO Mike Griffith said that over the holidays, Guitar Hero III: Legends of Rock became the first single game ever to surpass $1 billion in sales. The game launched in the fall of 2007."
Source: Activision statement, January 2009, quoted by Edge Online, 9th January 2009