From Halopedia, the Halo wiki
Genetically augmented humans wearing MJOLNIR armor, the ultimate super soldier.
Spartans are the crack infantry unit of the UNSC—tough, fast moving and equipped with a rapidly recharging energy shield when not in combat. Their enhanced agility and strength enables them to leap high into the air before slamming into the ground, either to take out an enemy, place an explosive device on an enemy structure or even hijack a vehicle.
Douglas-042 can be upgraded with his specialist weapon, which is a long range, slow firing rocket launcher.
Douglas-042 had a tough time adjusting to the SPARTAN-ll program as he had originally come from an affluent family in Khetleya on the Asphodel colony. He found the sudden culture shock difficult to adjust to, but soon focused that anger into a quiet confidence in his physical ability-even among the other Spartans Douglas is considered something of a giant, and he started to believe that he had a purpose in life.
This faith in destiny has given Douglas more of an optimistic outlook in life than the guarded cynicism common among other Spartans, and it is this hopefulness that helps lift their spirits in hard times.