Overlord

Overlord is the code name of an American command base that during combat gives information on the enemy's strength and location, as well as new orders or objectives to the soldiers currently in action.

Call of Duty 4: Modern Warfare
Overlord was the U.S. Command from Call of Duty 4: Modern Warfare during the U.S. Marine invasion of Al-Asad's country (labeled "Command" in the subtitles, identifying himself as "Overlook" at the beginning of "Shock and Awe"). He was last heard on the mission "No Fighting in the War Room", when all the S.A.S. teams were ordered to exit the base.

Call of Duty: Modern Warfare 2
Overlord gives orders to the US Army Rangers, particularly Hunter Two-One, in Call of Duty: Modern Warfare 2. He is heard in "Of Their Own Accord", "Wolverines!" and many other levels, including Spec Ops. He communicates objectives and commands to Ramirez's squad.

Call of Duty: Modern Warfare 3
Overlord also appears again in Call of Duty: Modern Warfare 3 giving orders to the Delta Force. He is also the Survival Mode announcer and the announcer for Delta Force in multiplayer. During the cutscene of "Iron Lady", his information and his connecting with the Presidential Aide ranks him as a General Commander.

Trivia

 * Overlord was originally the voice of the U.S. Army Rangers multiplayer announcer in Call of Duty: Modern Warfare 2, and can be heard announcing the AC-130 in the "Customized Killstreaks" trailer.
 * Overlord appears in and survives all games in the Modern Warfare series, along with Price and Nikolai.
 * His callsign in Call of Duty: Modern Warfare 3 is "Centcom Comm".
 * In Call of Duty: Modern Warfare 3, Overlord is most often heard in Special Ops, except in the mission "Milehigh Jack", where the announcer is Vladimir Makarov, "Resistance Movement", where the announcer is John "Soap" Mactavish and "Firewall", Where the announcer is MacMillan.
 * Overlord never made a physical appearance, he is only heard giving orders.
 * Overlord's new voice in Call of Duty: Modern Warfare 3 is never explained. It is possible there are multiple operatives under the callsign, similar to MacMillian and the unnamed Baseplate operative.