Who is Jacob Keyes from The Fall of Reach and what is their importance?

Jacob Keyes is a Lieutenant. He is assigned to pilot Dr. Halsey's vessel and protect her at the start of the novel. He also accompanies her onto the school playground to observe and run a test of Number 117 (John). Keyes' naval record is less than stellar.

Jacob's record for keeping a secret and remaining loyal to his commanding officer is the main reason Dr. Halsey chooses him as an escort. Over the years, he works his way back up in rank. He is the captain of the Iroquois when Halsey chooses him again to pilot the ship, Pillar of Autumn, for a new Spartan mission.