Wraith

Unit-137W is a robot who was a VI (virtual intelligence) at first but later on became a true AI (artificial intelligence), thus scaring the crap out of the scientists that created him. He was a failed experiment in that regard, and because of his endless ability to learn and adapt, the humans who created him categorized him as "highly dangerous" and that all encounters with him should be kept at minimum. After that he lost his arms, and nowadays he resides in the old station where the main laboratory is his nest. 

No-one really knows if Wraith is as hostile as the scientists said he would be. Maybe if someone was to treat him nicely, he would return the favor...