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The species inbound on Earth — beings of light-speech who cannot lie, will not stop, and have a single droplet's worth of patience for a species that thinks faster than it talks.
Trisolarans are an alien species refugees from a chaotic three-sun system. They evolved unable to lie — speech is broadcast light, every thought visible — which makes them swift, decisive, and structurally unprepared for human deception. The Wallfacer Project exists because of this asymmetry. The Trisolaran civilization treats its survival as a non-negotiable axiom and treats Earth's existence as logistics. By Book 2 they have already censored Listener 1379, launched the fleet, and seeded sophons over every human telescope; the only thing they have not yet done is take Luo Ji seriously.
Never directly described in canonical biological detail in The Dark Forest — appearances of Trisolarans are mediated through the Three Body game's iconography (figures in tunics on a dehydration plain), through Sophon's avatar in later books, and through the sound of light-speech rendered as text.
Also known as: the Three Body People, the San-Ti, 三体人