Codemasters is a British based video game development company founded in 1985. In the early 80's they primarily produced low-budget titles be eventually started producing full price games such as Micro Machines. After defeating the NES lock-out chip they released the Game Genie in 1990.
Interestingly, the Lead Programmer at Codemasters was once Bryan Black. However, this apparently was not the same Bryan Black who later emerged in the GameShark hacking scene as CodeMaster (and eventually CodeMasterX, or CMX). Hmm...