Nathan Marten is a character in DEXTER that is introduced in Season Three. He is a pedophile who approaches Astor Bennett while Dexter Morgan, Rita Morgan, and the kids were shopping at a grocery store. Later on it shows that he is sexually interested in Astor, and thus becomes a danger to Dexter's family.
Nathan is a moderately tall man with black hair and deeply tanned skin. His face has an unusual "childlike" flare to it as he smiles and stares at things, suggesting further towards how his personality of being a pedophile shines through him. His clothing is that of an upper-middle class individual, typically colored t-shirts with stripes and tan, khaki pants with dress shoes. He sometimes brings a professional camera with him, which most likely costs anywhere from $500 to $5,000.
Marten denies that he has anything to do with pedophilia, most likely to protect himself and his reputation...but if pressured, will admit to things he had done in the past and "claims" he has moved on. Unfortunately, this isn't the case and his personality is that of a perverted stalker who watches his prey from a distance.
He is the polar opposite to Dexter at the Hunt...while Dexter watches with a tiger's glare as he observes his target, Nathan watches like with a gentle tone, though obviously getting some sort of arousal from it. He doesn't seem to back down either when confronted...suggesting he's a more seasoned serial rapist than a serial killer.
Marten only appears for one episode in Season 3, as the focus of Dexter's attention during the episode.
While Dexter and his family shop at a local grocery store, Astor wanders off by herself and Dexter quickly follows to find out where she went. When he discovers her, she is talking to a much older man than herself (but closer to Dexter's age) with a very unusual feeling about him, from which Dexter picks up upon immediately as a predator much like himself, but for a different kind of prey. He rushes forward casually to confront the man, while making it seem like it's nothing when he talks to Astor. Nathan doesn't catch on to this immediately and instead stands firm as the two stare off...and both part ways shortly thereafter when Dexter points him towards what he "claims" he was looking for earlier. In the parking lot Dexter makes a note of Nathan's registration number.
Dexter decides to do some research on Nathan and it proves that his instincts are never wrong, he is a predator and a sexual one at that, convicted of molesting young girls. When faced with the decision to pursue killing him or not, he realizes it is a violation of the code of Harry and instead continues on with his life. That is until he watches Nathan taking pictures at a local beach with Astor running around in her bathing suit. It is then that he makes the choice to instead publicly confront him about his interest in Astor and his past. Marten denies any wrongdoing but Dexter is not convinced.
Later that night Dexter goes to Marten's home, where he find him looking at pictures of Astor he had taken at the beach. Dexter decides right then to strangle him, saying "nobody hurts my children" as he does so. Marten is one of the few victims Dexter has killed on impulse without taking the time to prepare a kill room and without the usual ritual. Unlike his other victims, Dexter gives Marten a chance to change and leave after being confronted and only kills him after seeing he disregarded his warning. The second time around, Dexter does not give him a chance to say anything.
Nathan Marten is one of Dexter's kills for Season 3, though he is not verified by the Code of Harry and instead is a violation, mainly killed out of impulse. To counter the fact that Nathan doesn't conform with the code, Dexter didn't preform his usual ritual to kill him. Instead, while Nathan was at home looking at the pictures of Astor he took on his computer, Dexter crept up behind him and strangled him with a garrote until he died. While Dexter was dragging Nathan's corpse out, he stole a carton of milk from his refrigerator, remembering that Rita asked him to pick up some milk for the kids.