Halo is a popular series of science fiction, 1st-person shooter video games developed by Bungie Studios and published by Microsoft. The games are set in the "Halo universe"-- a science fiction universe created by Bungie Studios exclusively for the series. Halo: Combat Evolved quickly became known as the 1st "killer application" for Microsoft's Xbox video game console when it was released in 2001, achieving both critical acclaim and financial success. Combat Evolved was later published on the PC and finally released for the Mac (for which it was originally developed prior to Microsoft's buying developer Bungie). In 2007, Halo 3 set a record by making 170 million dollars in its 1st 24 hours of sales.