Height: 7' 2" (in armor)
Weight: 1000 lbs. (in armor)
Age: Unknown
Background: Not much is known about the Master Chief after he was taken from his family and introduced into the SPARTAN-II project. His first name is John, and that is the only part of his name ever spoken in the series.

Height: Unknown
Weight: 0.0lbs.
Age: Unknown
Background: Cortana is the shipboard AI of the Pillar of Autumn, and Master Chief's companion throughout much of the series.

Height: Unknown
Weight: Unknown
Age: Unknown
Background: Keyes grew up on Earth (presumably America) along the coast of the Pacific ocean. He became a minor hero after holding the Covenant off of the UNSC Meriwether Lewis long enough for the ship to escape. After that he was chosen to lead the attack group on the secret mission planned to start from Reach.

Height: Unknown
Weight: Unknown
Age: Unknown
Backgorund: Not much is known about Sgt. Avery Johnson. Other than his name and the fact that he has a neurological condition which basically prevents him from getting infected by the Flood.