Martin Jackson

Martin Jackson is an entomologist and member of the original group of scientists. He served as the assistant of Ryan Lainus and after the latter's betrayal he stepped up and took the role of the main entomologist. He is a very anxious and socially awkward guy who accepted William as his protector and relied on others to keep him safe from the beginning. He is also very shy but dirty-minded, as he likes both Nora and Penny, but doesn't ever make a move towards any of them. He has very low self-esteem, which is why he doesn't flirt with the girls. 
Martin is one of the many who suffer from depression and anxiety. At first he is seen being unable to breathe many times and needs heelp from Christy. All the time though, he watches nora and Penny with the edge of his eye. He often thinks that it is pointless to keep trying and wants tto give up. At Nebraska, he is among the ones that want to leave for there, but since Ryan had already left, William didn't allow him to go. 
When he first examines a tracker, both he and Ryan are shocked by the perfection of the organism. Martin is distracted though from terror and worries he might get infected with something. Overall, he doesn't provide anything useful during that test. 
Jack notices how he looks at the girls, and knowing his type, he engages a friendly talk. He starts about how much the girls want to get laid now that their psychology is fragile. He goes on and pours him more and more alcohol, until he convinces him to go and hit on them (Since Ryan was considered dead, Jack said women wet their panties for a grieving man who has lost his friend). Martin hesistates at first, but Jack gets more dirty, describing some dirty things he has thought and it is revealed that Martin has a dirtier mind. Having found someone to laugh at, Jack convinces him to go hit on them hard, like catch their boobs or something. Martin is hesistant at first, but in the end he goes, pulls them both close and grabs their asses. They both punch him at the same time, while Jack falls of his chair laughing. The girls realise what is going on and forgive him. Penny then hooks up with Jack. 
Until Ryan is gone, he helps him with everything and is friendly with Lydia and her son.  
After his rejection and when Ryan was considered dead, Martin's psychology worsens and he attacks Jack out of the blue. he takes a fire extinguishher and hits Jack on the head, throwing him down from his chair. Jack stood up to hit him back, but others got in the way. Martin tossed the extinguisher and left, while Jack yelled that he is a dead person. William then ordered Jack no rertibution 
Later he believes in himself, when he discovers a piece of useful advice during an autopsy. This discovery leads him to gain self confidence. Until the final battle(????), he will be able to use firearms. 
William scolds him for the event, but Martin yells back, saying that William has no right to talk to him like that. He says William has his whole family there while he couldn't bring anyone himself, and his parents and siblings are most probably dead now. William doesn't sit to listen to him, tells him that they have an important mission and to pull his shit together. 
At the decision for Nebraska, he wants to go with the group there, but William doesn't allow him to, and the group, who had talked to William before, told him he wasn't invited. Martin is heartbroken over this, but stays back 
When Penny is blinded, he helps her with everything, and even has sex with her once, but Christine scolds him.  
At some point, the house they stay into is overrun and he escapes by leaving Penny behind to be eaten.  
At the military base, he makes some important discoveries regarding the aliens. 
in the end of the military encampment, when Ryan is captured, he convinces Martin that the aliens are there to keep only the best of the best of the humans and he might be one of them. Everything Ryan says makes sense, but scared as he is, and believing the human race is doomed, Martin shoots himself on the head.