From Halopedia, the Halo wiki
Gearbox Software is a video game developer founded by Randy Pitchford, Stephen Bahl, Landon Montgomery, Brian Martel, and Rob Heironimus in January of 1999. They are located in Plano, near Dallas, Texas. Gearbox was responsible for the PC port of Halo: Combat Evolved and the making of Halo Custom Edition.
They are best known for a number of high-profile PC and console games such as the Borderlands series, the Brother in Arms series, the Half-Life expansions Opposing Force and Blue Shift, and Aliens: Colonial Marines.