From Halopedia, the Halo wiki
Echo23023 is an individual known only by his last initial (E, delivered in the alphabet) and what appears to be a fraction of his serial number. He is a member of the Office of Naval Intelligence of a high enough rank to be familiar with the Spartan-I Program. On September 12, 2552, he and another individual known as Mike44236, also with ONI, shared a sub-chatter conversation involving the interest of Catherine Halsey and James Ackerson in Avery Johnson.
List of appearances