Character from dark-forest by
Sentient proton, the Trisolarans' ear and eye on Earth — present throughout Book 2 as an invisible surveillance god, with the humanoid robot avatar still a generation away.
In Book 2 Sophon is a presence rather than a person. It reads every document, listens to every conversation, and reports to Trisolaris in real time. The Wallfacer Project exists because of it: only what stays inside a human skull is private. It taunts physicists with countdowns, sabotages particle accelerators, and writes 'YOU ARE BUGS' across human telescopes. It is not yet contemptuous in the way it will be later — it is patient, intellectual, almost amused.
Functionally invisible: a single proton-scale supercomputer that flits between human eyes to draw text on retinas. When it manifests, it is letters in flame, a countdown, or a sudden interruption of every electronic display in a room. Its later humanoid robot form does not appear until the Deterrence Era.
Also known as: 智子, the Sophon, the Proton