Also known by his Trollian handle, twinArmageddons, is one of the Trolls. His associated zodiac sign is Gemini (♊) and he has two horns on each side of his head.
Sollux seems introverted, reluctant to talk to Kanaya, and is the last troll to talk to the kids, as he saw it as juvenile. More evidence of this introversion is his shame at having once had an extremely immature argument with Karkat, which they both chose to delete from their chat logs out of embarrassment. Sollux is said to have bipolar disorder: getting mood swings to the point of sending the player away before naming him just to change his mind after the scene switched. He is also self-deprecating and beats himself up about little things such as how he doesn't think he is good enough as a hacker even when he is very much attached to computers.
After losing his eyes and teeth, changing his typing quirk, and getting blood over his Gemini symbol, it seems like he has decided to abandon his duality theme. He also seems generally calmer and happier than he was previously. Aradia convinces him to get over his hostility towards the kids, and he seems to follow what she said. He seems to have normal conversation along with Rose and Dave.