A young boy was kidnapped by Abstergo Industries, a front for the Templar Order, and taken to a secure facility in Philadelphia. Under the designation of Subject 4, he was placed in the Animus. While Subject 4 was locked into this device, Dr. Warren Vidic harvested his genetic memories and experimented on the young boy's mind.
They gave the boy a false identity and implanted a single hidden impulse: locate and kill the Mentor of the Assassin Brotherhood. With the initial phase of the Templar plot complete, the boy was cast out from the laboratory and left to fend for himself, but not before being given a new name: Daniel Cross.
A traumatized Daniel was discovered by the side of a road, barely dressed and speaking in Russian.