Marcus Lehto

Lehto in the Halo 3 Announcement Trailer documentary.

Marcus Lehto is a senior employee at Bungie Studios. He is Halo's Art Director and the man who created the models for many of the objects seen in the Halo universe, including the Master Chief, Captain Keyes, and Scorpion models in Halo: Combat Evolved. He has attached several easter eggs to his models, including his birthday on the Scorpion tank and his initials on the boot of the Master Chief. Also, the faces of the Cavemen of Sierra 117 are probably inspired by his face.

He returned to help produce Halo 2 and redesigned many of the models for new characters, including the new Master Chief and Elite armor.

He is currently working as the Art Director of Halo: Reach.

Trivia

On Halo: PC, before the background animation begins, there can be seen the letters Gny Sgt Marcus, referring to Gunnery Sergeant.
Lehto is a Finnish name, suggesting that Marcus is of Finnish origin. He has probably contributed to many references of Finland in Halo, such as Esko Korpijaakko (Korpi and Lehto are different kinds of forests) and Summa Deep Space Incident.
Marcus is sometimes known as "The Easter Egg King".
A Marine face model variant (entitled "Marcus" while viewed in Halo Map Tools) in Halo: Combat Evolved looks similar to Lehto's.
A possible reference the above fact is that if you edit AI properties (in Sapien, part of the HEK), you can see under the "leader" field that you can set it to either Sgt. Johnson or Sgt. Lehto, or random.
In college, his hair resembled the fashionable "Richard Marx."
The face seen under all of the Spartan helmets in the Halo 3 Beta are actually models of Marcus's face.