The Contractor (His name is unknown) is an ambiguous and shady character in Far Cry 2.
The Contractor is never seen in-person in the game, only being heard when he speaks to the player character over the phone. Each time the player starts an Assassination Mission, the Contractor will call the player character and give him the details of an "available target of opportunity" that needs to be assassinated, and promises rough diamonds as a reward upon completion. To add to his mysteriousness, his voice is masked using a voice changer, making it distorted and hoarse.
Outside of the Assassination Missions, the Contractor is only heard once more if the player has the Bonus Missions installed (obtained through a serial key). At some point in the game, usually if the player enters a town, the Contractor will call the player character and inform him that he knows of his hunt for The Jackal. Furthermore, he tells the player character that there was a mercenary tasked with the same mission before him who had been KIA, leaving behind a set of tapes. The Contractor tasks the player character with hunting down the tapes in order to find and kill the man responsible for the mercenary's death.
Due to his role in the game, it is likely that he is the player character's employer who gave him the mission of assassinating The Jackal. This, however, could also be unlikely, as it is stated by The Jackal in the opening mission that the player character was "fired" for failing on the contract (which would cut all ties between him and his employer).