He took on a protege named Peter Thornton, however, he never let him kill anybody.
As a young man, he had attractive features with long, wavy hair and a face ready for the world. When he grew older, his face became wrinkled and his clothes matched that of a professor in his work. After he had just killed someone, he would usually wear rubber coveralls while in a swamp disposing of the body parts.
Having been responsible for someone's death at a young age, he has grown up with killing tendencies and has practiced these urges on students taking his course (typically female). It is assumed he also rapes them before he kills them, as some were found naked...while others he disposed of in a nearby swamp for alligators to feast on. Apparently he cared enough about his killings to try and teach another man the tricks of the trade, having an apprentice named Peter Thornton.
Just some time after Harry Morgan's death, Dexter attended college and took a course with Dr. Robert Milson. He knew about Milson back when he was called "Bobby" through some of Harry's old case files and found out about his earlier transactions, which included murdering his girlfriend. His lawyer was able to convince everyone that it was just rough sex gone wrong and had his record expunged. Through a little further research, Dexter also discovered that Milson was behind the deaths of seven missing female co-eds in his course. Dexter was ready to kill him, so he waited at night with a line of fishing wire when Milson went for something to eat at a vending machine...Dexter pulled him along until he was rendered unconscious (but made sure to grab the chips before he left).
Dexter made quick work of Milson, shoving his blade into Milson's heart and killing him, though little to Dexter's knowledge...Peter Thornton was watching him from the shadows. Dexter went on to cut up the body and leave it to be feasted upon by alligators in a nearby swamp..oblivious to someone following him. Later on Dexter is faced with the reality that killing Milson in the open like that warped young Peter further, allowing him to go ahead and kill Jenna Lincoln while watching from a window. Dexter hurries to try and figure out who this boy is, later realizing that he killed his own father at a young age and may be responsible for other murders...so Dexter confronts him, learning that he was Milson's apprentice and was never allowed to kill the girls. Even after technically letting him go, Peter kills again and this forces Dexter to take his life...thus preventing his "copy" from going on and killing more innocents.
- Unknown girlfriend in his teens
- Seven co-eds as an adult