The Four Horsemen

The Four Horsemen is the name for a group of four men whose aims appear to become the dominant world power and usurp the United States. They are named after the Four Horsemen of the Apocalypse. It is the player's objective throughout Call of Duty 4 to uncover information on them and eventually eliminate all four. They all have some form of command role in their respective groups. Four Xbox 360 achievements are associated with them, as the player gets an achievement each time they complete a Veteran-level mission that a Horseman dies in, the only exception being The First Horseman, as it is not confirmed that he did die.

The First Horseman
The First Horseman is a somewhat mysterious individual who works for/with Al-Asad, though to what extent is unknown. He is apparently killed during the final fight in the capital, either during the battle or after the nuclear weapon detonates. The only visual reference to him is seen afterward in a photo, showing all Four Horsemen meeting. In the photo, the Fourth Horseman, Imran Zakhaev appears to be directly speaking to him. It is speculated that the First Horseman is a go-between for Al-Asad and the Ultranationalists, possibly also serving as a poltical or financial adviser to Al-Asad. "The First Horseman" is also the name of an achievement in the Xbox 360 version of the game. This achievement unlocks when the player beats the level Shock and Awe on Veteran difficulty. It is believed that this horseman didn't die as there has been assumed deaths before in this series, a good example is the fourth horseman.

The Second Horseman
The Second Horseman is Al-Asad, the leader of an unnamed Middle-Eastern nation following a bloody coup. He is an ally of Imran Zakhaev. He detonated a nuclear bomb in the capital, killing many of the invading U.S. forces. Later killed by Captain Price in the twelfth mission Safehouse. Beating said mission on any difficulty unlocks “Wrong Number”, while beating it on Veteran awards “The Second Horseman”.

The Third Horseman
The Third Horseman is Victor Zakhaev, the son of Imran Zakhaev. Victor is the commander of the Ultranationalist military forces on the ground in Russia. He committed suicide before he could be caught in the sixteenth mission, Sins of the Father. The achievement “Desperate Measures” is achieved simply for beating Sins of the Father on any difficulty, while “The Third Horseman” is achieved for beating Sins of the Father, and the previous mission “Heat”, on Veteran.

The Fourth Horseman
The Fourth Horseman is Imran Zakhaev, a Russian Ultranationalist and leader of the "Horsemen". He supplies Al-Asad with weapons, including a nuclear weapon. He was thought to be dead 15 years before the main events of the game, having been shot by Lieutenant Price and Captain MacMillan, however he lives this encounter losing only one of his arms. He is killed by Sergeant Soap MacTavish in the final mission Game Over. The Achievement “The Fourth Horseman” is awarded for completing said mission on Veteran.