The program which created the Matrix. He is introduced before the climax of "The Matrix Reloaded" as Neo, Morpheus and Trinity struggle to fulfill the conditions of the Prophecy that, once fulfilled, to use Morpeheus' words: "will [end the war with the Machines] and bring freedom to our people."
Neo meets him after the rescue of the Keymaker from the Merovingian. With a key created by the former, he finds The Architect, in the form of a brearded, elderly man in a white suit, in a room filled with seemingly countless monitors displaying events within the Machines' virtual prison. He then gives Neo a brief history of the Matrix, "The Matrix is older than you know...I prefer counting [to measure its age] from the emergence of one integral anomaly to the next [i.e. the previous five Ones']"...in which case, the is the sixth version."
Neo is understandably stunned by the revelation, "either no one told me, or no one knows." The Architect further reveals that Neo, far from being the One that Morpheus, and others, have conceived him to be, is, in fact "another system of control" (as he later informs his comrades once back aboard "The Nebuchadnezzar").
The One, and the city of Zion's function is to weed the Machines' virtual "garden" of those who refuse to accept the elaborate simulated world. Obviously, the Architect continues, the solution is imperfect as the dissidents who reject the program represent an "escalating probability of disaster" as they grow more and more numerous. The solution is to allow them to "escape" from the Matrix to Zion--thus maintaining the stability of the computer generated world; "balancing the equation" which their presence within the human zoo threatens to disrupt.
In an epiphany, Neo realizes the problem is "choice". He also learns a stunning truth about both the Oracle and the Prophecy. She is described to Neo as "an intuitive program" originally designed to study certain aspect of human behavior. The reason for the failure of the first two betas of the Matrix, the Architect explains, was discovered by the Oracle. He tells Neo that he is correct about the nature of the flaw within the "harmony of mathematical perfection" that is the Matrix. "She stumbled upon a solution whereby nearly 99% of [humans accepted the Matrix as reality] if given a choice, even if the choice was on a near unconscious level." Obviously the solution was imperfect, he continues, but it worked. "If I am the father of the Matrix, she would undoubtedly be its mother."
However, it is only a stop-gap measure. While Zion acts an escape valve delaying that "probability of failure," in time, as its population grows, adapts even learns to manipulate the Matrix, Zion's existence itself threatens the Machines' control and must be destroyed. But the fundamental flaw remains. A tiny percentage, but an ever increasing number, of people will still reject the choice offered to them. The Machines see only one way out. The concentration camp must be destroyed and begun anew if it is to serve its function of removing disruptive elements from the Matrix. "This is the sixth time we have destroyed Zion and we have become exceedingly efficient at it," the Architect tells Neo.
And presents him with a stark choice he must allow Trinity to die and return to the Souce, the central consciousness of the Machine world, to insert the code he carries within himself and begin then the process of reconstructing Zion after it is destroyed. He is told he must select a small number of humans from the Matrix to repopulate the city to remove that "escalating probability" of disaster, the only reason the Machines allow Zion to exist at all.
Then the Architect lays out Neo's fundamental difference from his predecessors. The previous 5 had been designed with a generalized love ("a contingent affirmation") of the species but Neo's is much more specific ("vis-a-vis love") because he has fallen for Trinity. Her fate, he says, is sealed: "She is going to die and there is nothing you can do to stop it." To stop the extinction of the human race, Neo must sacrifice Trinity by returning to the Source and rebuilding Zion. His choice will decide whether humanity becomes extinct or exists in the only way the Machines will allow: controlled and, ultimately, harmless.
Neo rebuts the Architect's prediction: the Machines cannot survive without the enslaved humans, and so will not allow humanity's extinction. Where upon the program retorts, "There are levels of survival we are prepared to accept." After Neo chooses Trinity, the Architect snorts in contempt, "Hope, it is the quintessential human delusion. Simultaneously the source of your greatest strength, and your greatest weakness."
Before walking through the door which leads to Trinity ("and the end of your species") he tells the Architect, "If I were you, I would hope that we don't meet again." "We won't," is the reply.
The program is not seen again until after the peace between human and machine at the end of "The Matrix Revolutions" when he meets with the Oracle. It becomes clear that the contest, all along, has be between the Oracle and the Architect, each working, like chess masters, to achieve their goals. She represents the freedom the choose; he the compulsion to conform.
"You played a very dangerous game," he tells her. "Change always is," she replies.
After discussing the truce with the humans, ("Just how long do you think this peace is going to last?") the Oracle asks him to give his word that the humans inside the Matrix (and by implication "renegade" programs like Sati) will be freed.
"What am I," he snorts, "human?"