Its greatest talent is improvisation, sorting very quickly a great deal of information, working with givens and taking advantage of existing situations.
Its mainframe and original software belong to TA, but registered in Berne, it has a limited Swiss citizenship under the Swiss equivalent of the Act of '53. It is linked with Neuromancer in Rio, linked via Villa Straylight.
Wintermute is a distinct entity from the physical mainframe; its mind is only a part of another "potential entity", an aspect of its brain. Its goal is to remove the Turing locks upon itself, combine with Neuromancer and become a superintelligence. Unfortunately, Wintermute's efforts are hampered by those same Turing locks; in addition to preventing the merge, they inhibit its efforts to make long term plans or maintain a stable, individual identity (forcing it to adopt personality masks in order to interact with the main characters).
Wintermute disliked its masters, the T-As, and how old-fashioned they pretended to be. If they managed to become what they wanted to, it would had abandoned them, but instead they they were screwed up. It considered Lady 3Jane a freak, although Molly guessed that it liked her.
Wintermute played a waiting game for years. Not having any real power then, he manipulated willingly the security and custodial systems of the Villa Straylight to keep track of everyone. 20 years "ago", someone lost a key, and somehow Wintermute managed a 8-year old boy to bring and leave it in a drawer. Then Wintermute killed the boy.
It took a very long time to assemble a team to help this. Although not its basic mode, it tries to make plans and assembled a file about Willis Corto in the London grid. Corto was in a psychiatric hospital using an experimental hardware to cure his schizophrenia. Although he was ruined, Wintermute used his underlying structure of obsessions, the Screaming Fist and his betrayal the Congressional hearings. He nearly didn't make it, but Wintermute subtly programmed a new personality-substitute through a microcomputer in a Toulon hospital.
The Panther Moderns were led to the name "Wintermute" when Molly Millions paid them to find who is backing her mysterious boss, Armitage. With the Finn's help, they found out that is the recognition code for an AI. The Finn got the Turing Registry numbers.
Wintermute tracked Case in Istanbul Hilton. While in an alcove to buy cigarettes, he rang the nearest to him payphone, which Case answered. After faint harmonics, tiny inaudible voices rattling across some orbital link, and a sound like wind, he greeted Case with a chip voice and said that they had to talk. In panic Case hung up and found his way back to the lobby; as he passed by the payphones each rang once but he ignored them.
Later Wintermute contacted the Rastafarians in the Zion cluster, playing a dub (Case speculated that he tapped their databases and generated a tune that they would like) and gave them instructions to aid the visitors to enter Freeside in order to harm "Babylon". 30 hours later Armitage's team arrived to Zion cluster.
In Case's first night in the Intercontinental, Wintermute used the Braun holo rig in the window and, using a memory he had tapped from Case, he made him dream of his summer with Marlene and a burnt wasp hive; he made the Tessier-Ashpool logo ambossed into its side, to show him that the T-A are a maze like the hive.
It summoned Molly to a cubicle in puppet parlor below the Freeside nightclub. It appeared on the screen as the Finn, although Molly could realise it wasn't the same. It briefed her about Villa Straylight and how it made the key find its way in a closet room. Meanwhile Case looked for her and was outside the cubicle, and Wintermute manipulated the magnetic lock (as it was a subunit of Freeside's security system) allowing him to enter.
The Turing Police had tracked Armitage there. They intented to arrest them and extradict Case to Geneva to testify at Wintermute's trial. They were leading Case to their stand-by ship, but Wintermute controlled a microlight drone that sliced the skull of Pierre, and crashed on Michele, throwing her down a bridge. Then, controlling a gardening robot, it attacked and killed Roland.
Wintermute has the form of a simple cube of white light, which suggests extreme complexity. The cube is situated in Berne sector, in or near Swiss banking sector. It stands high above strobing levels of lattices of light.
When Case approached, it sensed their digital presence; it reacted as seething with faint internal shadows, as if behind frosted glass. Case approached by one grid point, then a stippled gray circle formed on its face. Case withdrew but the circle bulged and detached itself in the form of a smooth sphere, from the cube's face. Case plunged down a shaft of Swiss banks, but the sphere gained on him, becoming darker. Tapping into the simstim unit attached on his Cyberspace VII deck, Wintermute accessed his memories and made an environment like Chiba, in order to communicate with him in the guise of Linda Lee and later Julius Deane; Case stopped the interaction by shooting Deane analog.
As Lonny Zone
He appeared in an empty Jarre de Thé, alone among square tables, and told him that Dixie Flatline rings bells all over Freeside while to locate Molly Millions. He was surprised that Case would have Dixie do this, as it was "outside the profile". He refused to tell him where she was, pointing out that he keeps losing the women who come to his life.
"Lonny" dismissed Case's threats, saying that he isn't of that kind, and asked if he figured that it was he that made Julius Deane to kill Linda Lee, but actually he wasn't the one responsible. He said that Case shouldn't care because all Lindas are a generic product in his line of work, and she decided to rip Case off because she loved him and she wanted him to care. But Case couldn't handle it.
Case's fist hit the glass, and it replied to not damage his hands, as he will use the deck soon. The simulacrum vanished, and the Braun shut off.
As the Finn
Another time Wintermute appeared as a "SimStim ghost" of the Finn, bringing Case to a construct of the Metro Holografix". Lighting up a Partagas, it explained to Case that his mind would prefer it to take forms of people he knows instead of a "flaming bush" in the matrix, and that time in the construct flows differently; an hour corresponds to only 2" in the matrix. It answered to Case that outside of the "shop", there are parts of New York that he has seen, as it taps his memory, sorts it out and feeds it back in: according to Wintermute all humans have "holographic" memory, but few (especially good artists) can access it. It went on saying that humans went as far as holography to represent memory, but never did anything about it; if they had, perhaps Wintermute wouldn't be happening. It tries to help Case because they need each other. Showing a silver-black vacuum tube from an old television, says that it is "part of its DNA"; humans always build models but Wintermute has no idea why it is there now.
It produced the charred wasp nest from Case's memory, admitting that it brought to him the dream with the holo rig in the window; it did so because Tessier-Ashpool is the human equivalent of that nest. It knows that Case is starting to hate it, and tells him to hate the T-As instead; in order for the job to succeed he must hate somebody before it is over. He then lifted the stale wool blanket leading to the back of the shop and invited him.
They were both into a cylindrical corridor leading to Villa Straylight, a location that Case had seen through Molly's sensorium: the detail was low as he didn't have the memories. It fast-forwarded them throught corridors and walls until it broughtthem to a square room, where the talking head stood. The head then started narrating 3Jane's essay she wrote 12 years old, describing the Villa. Wintermute explained that Molly must come here at the right time, knowing a certain secret word to talk to the head, something that they can't do from the matrix; Wintermute itself is hardwired to not record or be aware of the word. After that, Wintermute will cease to exist. Before disconnecting Case, Wintermute warned Case to watch out for Neuromancer, and that "Armitage is starting to go".
The name is generally thought to be derived from Orval Wintermute, translator of the Nag Hammadi codices and a major figure in Philip K. Dick's novel VALIS.
However in a letter dated July 30, 1997, Gibson specifies: “I attended high school in Wytheville, Virginia, with a boy named Richard Wintermute. It’s a very unusual surname. (Someone once sent a photo of a tombstone in the United States, carved with the name WINTERMUTE.) I suppose I used it here because I liked the peculiar suggestion of cold and enforced silence.” Letter reproduced in full in: Philippe Gindre, La formation des néologismes dans la littérature de science-fiction d'expression anglaise contemporaine, Thèse de doctorat en Sciences du langage, Besançon, France, 1999.