Overlord

Overlord is the callsign of an American command base that during combat gives information on enemy strength and location, as well as new orders or objectives to soldiers 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). He was last heard on the mission "Shock and Awe" after the nuke exploded.

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 "Team Player", "Of Their Own Accord", "Wolverines!" and many other levels.

Call of Duty: Modern Warfare 3
Overlord will also appear again in Call of Duty: Modern Warfare 3 giving orders to the Delta Force, but this time he is voice by a different person.