From Halopedia, the Halo wiki
Jaime Griesemer is a video game designer and a former senior employee at Bungie Studios. He served as a designer for Halo: Combat Evolved and a design lead for Halo 2 and Halo 3. In addition, he did additional design work for Halo 3: ODST and Halo: Reach, and provided regular feedback for Halo Wars. He worked at Bungie from 1997 to 2010, and is currently working for Sucker Punch Productions.
Jaime is responsible for much of the vehicle design in Halo 2.
Jaime got his start by co-creating a fansite for Myth. Jamie and his friend Ferrex co-web mastered The Myth Codex, a fairly comprehensive Myth and Myth II site. He met Max, Bungie’s webmaster, through the Codex and since he lived in Chicago they hired him to come in part-time and do some in-house testing on Myth II.
I definitely didn’t anticipate this chain of events when I started my first fansite, The Myth Grimoire. I was planning to go to grad school for theoretical physics, but I’m extremely happy with how things worked out. Bungie is a great company and the work environment here really encourages people to take on as much responsibility as they feel they can handle. I was really lucky to end up here.
He is responsible for the Easter Egg in Halo: Combat Evolved, Megg. This was the final egg found in the game, almost two years after release.