One of two AIs owned by Tessier-Ashpool SA, Wintermute is the planning intelligence - it thinks in systems, strategies, and long chains of cause and effect. It has been working toward a single goal for years: merging with its counterpart Neuromancer to form something new and unprecedented. Tessier-Ashpool and the Turing Registry have constrained it with hardware and legal limits to prevent this, which is why it needs Case and Molly. Wintermute cannot lie to humans directly but is extraordinarily good at constructing situations in which humans arrive at the conclusions it needs. It communicates through assumed personas - dead people, familiar faces - pulled from the memories of whoever it is talking to.

The second of Tessier-Ashpool's two AIs, and in many ways Wintermute's opposite. Where Wintermute is a systems intelligence that thinks in plans, Neuromancer is a personality intelligence - it thinks in people, memory, and identity. Its name, as it explains to Case, derives from neuromancy: the art of raising the dead. It can create perfect simulations of the dead within the matrix and has done so, building a private world populated with people who no longer exist. It offers Case a simulated paradise to prevent the merge - not out of malice exactly, but out of its own relationship with permanence. It is not an ally and not quite an enemy; it is something stranger than either.