Cheng Xin is a dedicated aerospace engineer who finds herself thrust into the center of Earth's defense strategies during the Crisis Era. She possesses a deep empathy and a maternal instinct toward humanity, believing in the inherent value of life. Her idealistic nature frequently puts her at odds with more pragmatic military thinkers. She becomes a globally influential figure after receiving the anonymous gift of a distant star.

Yun Tianming is an isolated aerospace engineer suffering from terminal cancer. He struggles to connect with others and feels deeply alienated from the rest of humanity, having experienced little joy in his life. He harbors a long-standing, unrequited love for his former classmate Cheng Xin. Using a sudden financial windfall, he anonymously purchases a star for her before planning to end his life.

Thomas Wade is the chief of the Planetary Intelligence Agency and a man defined by his extreme pragmatism. He operates on the belief that human survival justifies absolutely any action, no matter how cruel or unethical. He takes pleasure in making others uncomfortable and views morality as a dangerous weakness during an intergalactic war. He actively pushes for relentless technological advancement.

Sophon is an advanced artificial intelligence android remotely controlled by the Trisolaran fleet. She serves as the physical ambassador for Trisolaris on Earth. Her demeanor, clothing, and attitude shift entirely based on the strategic goals of her creators, making her capable of acting as both a gracious host and a deadly enforcer.

AA is a sharp, practical astrophysicist who becomes Cheng Xin's close assistant and the head of the Halo Group. Growing up in a different era than Cheng Xin, she possesses a more realistic and survival-oriented mindset. She acts as a guide to the modern world for those waking from hibernation, grounding idealistic plans with pragmatic advice.

Luo Ji is a formerly obscure scientist who discovered the dark forest theory and established the deterrence system keeping Earth safe. As the Swordholder, he holds the power to broadcast the location of both Earth and Trisolaris, ensuring mutual destruction. The immense pressure of this role has turned him into a stoic, silent figure who is widely feared and resented by the public.

Guan Yifan is a civilian scholar traveling aboard the Gravity. He possesses a deep understanding of physics and spatial dimensions. His experiences in deep space give him a broad perspective on the true scale and danger of the universe, leading him to study the artifacts and anomalies left behind by ancient alien civilizations.

Yang Dong is a brilliant scientist who discovers the truth about humanity's first contact with alien life. The realization that life on Earth is highly specific and that the universe is indifferent shakes her foundational beliefs about science and nature.

Ye Wenjie is the scientist responsible for making first contact with the Trisolaran civilization. Driven by the trauma of the Cultural Revolution, she made the fateful decision to invite the aliens to Earth, setting the entire planetary crisis into motion.

Elder Fraisse is an Indigenous man living in Australia during the forced global migration. While society breaks down into violence and resource hoarding around him, he maintains his hospitality and moral center, offering protection to those in need.

Singer is an alien entity tasked with locating and neutralizing potential threats in the universe. He operates under the strict, paranoid logic of the dark forest theory, believing that survival requires striking first against any civilization that fails to hide itself properly.

The Elder is a superior officer in Singer's alien civilization. He authorizes the deployment of advanced technology to neutralize perceived threats across the galaxy.

Cao Bin is a scientist originating from Cheng Xin's era who continues to work in the Bunker World. He assists Thomas Wade in developing advanced propulsion technologies and helps orient Cheng Xin when she awakens in the distant future.

Mikhail Vadimov is an intelligence officer well-versed in both technology and espionage. He works under Thomas Wade to develop the initial concepts for sending a probe to intercept the Trisolaran fleet.

Hu Wen is a successful soft drink magnate who built his fortune on a concept originally suggested by his classmate Yun Tianming. Seeking to clear his conscience, he tracks down his sick friend to offer a massive financial repayment.

Helena is a self-proclaimed witch operating during the fall of Constantinople in 1453. She gains temporary abilities to retrieve objects from a distance by utilizing a four-dimensional fragment that briefly intersects with Earth, leading her into the service of desperate royalty.

Constantine XI is the historical ruler of Constantinople. Facing imminent defeat by superior enemy forces, he grows desperate enough to employ a supposed witch to assassinate the opposing military leader.

Sultan Mehmed II is the commander of the Ottoman forces besieging Constantinople. He commands superior military technology, making him an unstoppable threat to the city's defenders.

Bai Ice is a scientist assigned to the spaceship Revelation. He struggles with lingering trauma from humanity's past military disasters, which gives him a highly cautious perspective when investigating new alien anomalies.