After leaving the briny world of oceanography, Greg joined the saltier world of games. He got his start in the gaming industry as a game designer at Ensemble Studios, where he worked on titles including Age of Empires: The Rise of Rome, Age of Empires II, and Age of Empires III. He then joined Blizzard Entertainment, where he was the lead systems designer on World of Warcraft for several years where he was best known for promising players a pony and nerfing Retribution Paladins "TO THE GROUND BABY."
Greg joined Riot in 2013 as the Lead Gameplay Designer for League of Legends where he managed the teams in charge of new champions, champion updates, game balance and ranked. He later became the Design Director for League of Legends where he worked with the other leads to help define the long term strategy for League of Legends and was accountable for the design quality of the game. He then became the Head of Creative Development at Riot where his team worked on Arcane, Realms of Runeterra, Riot Forge, Tales of Runeterra, K/DA and the partnership with Marvel Comics. On December 17th, 2020, he announced that he would be leading the development of an MMO set in the League of Legends universe.