Warning: This bio may contain most definitely contains spoilers.
Carl Grimes is the son of Rick and Lori Grimes and older brother to baby Judith (born in "Killer Within", S3 E4). When first seen in Season 1, he is just a shy kid of around twelve years old who idolizes his father, is close to his mother and Shane, and is friends with Sophia. Lori tries her best to shield Carl from the horrors of this new reality. Despite the terrible world he now lives in, Carl is still a kind boy and comforts those around him to the best of his abilities.
At the beginning of Season 2, Carl shows signs of wanting to take a more active role in the group. He doesn't want to be seen as a burden and wants to help the others. After being shot, he changes. Though remaining bold, Carl's belief in God falls away completely and he begins acting cold and a bit more cruel. His boldness become recklessness when his actions unintentionally free a walker that ends up killing Dale. Carl cries and feels immense guilt, never wanting to touch a gun again. It is only after Rick talks with him that he realizes he will have to use a gun to survive in this new world. He overcomes his reluctance to use a gun when he shoots the reanimated Shane, who creeps up on Rick.
By Season 3, Carl is more like a child soldier, seasoned from fighting walkers alongside the group while on the road. His shyness has faded and he is significantly more mature. Despite this, he still cracks an occasional joke and gets exasperated when his mom tries to restrict him from helping the group. After he is forced to shoot Lori to keep her from reanimating, Carl becomes cold and distant to others, speaking only when he feels the need. This coldness finally culminates in him killing a surrendering boy from Woodbury, which opens Rick's eyes to Carl's negative emotional being.
In Season 4, Carl is around fourteen and has relaxed a great deal, due to Rick's request that Carl live as normal a life as possible. Carl enjoys normal things such as socializing with others his age and reading comic books, but retains his maturity and his feelings towards walkers. Even though it is difficult for him to try to be normal, Carl does his best to please his father. When things begin to take a turn for the worst around the prison, Carl asks for his gun back, knowing he will need it. Carl has a big role in the defense of the prison, helping his father keep walkers out. After the prison is destroyed by the Governor and his group, Carl begins to fill with anger and sorrow for the loss of the prison and the members of their group and angrily blames Rick, but later realizes that it isn't all his father's fault and that he needs Rick, revealing his fear for the situation they are in.