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 Russian Federation and start a war in the United States. They are named after the Four Horsemen of the Apocalypse. It is the player's objective throughout Call of Duty 4: Modern Warfare to uncover information on them and eventually eliminate all four. They all have some form of command role in their respective groups. Achievements are associated with them, as the player gets an achievement each time they complete a mission on Veteran 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.

The Second Horseman
The Second Horseman is Khaled 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 (30,000, as Shepherd later revealed). He is later killed by Captain Price in the twelfth mission "Safehouse". Zakhaev later deployed a large number of Ultranationalists to rescue him, but it was too late. Beating this 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 survives this encounter and "only" loses his left arm. He is killed by Sergeant John "Soap&quot; MacTavish in the final mission "Game Over". The Achievement “The Fourth Horseman ” is awarded for completing said mission on Veteran.

Trivia

 * The Four Horsemen is likely a reference to the Four Horsemen in the Bible, warning the world of the apocalypse. Their names were Pestilence, War, Famine, and Death, and their colors (in the same order) were White, Red, Black, Pale and the riders carry a Bow, a Sword, a Balance (Much like the one that represents Modern day Courts), and a Scythe, and their powers being that the first conquers through means other than war, the next being to take away peace from the world, the third being to bring famine to the world, and the fourth being "over a fourth of the earth, to kill with sword, and with hunger, and with death, and with the beasts of the earth". It is unknown if each character represents each one of these evils.
 * The three Horsemen that can be seen in the game are all killed by an M1911 pistol, and all, but Victor are killed with Price's M1911. Khaled Al-Asad is killed by Price's M1911, Imran was killed by Soap with Price's M1911 and Victor Zakhaev killed himself with an M1911 pistol.
 * Al-Fulani, Soap, Captain Price and Gaz are the only ones who saw the three known horsemen in person.
 * The titles of horsemen can be found in Modern Warfare 2 files. However, they are not present in game.
 * The intro of S.S.D.D. in Modern Warfare 2 shows a statue of Zakhaev on a horse, fulfilling his role as the Fourth Horseman.