Although Jax had a crucial role in Sons of Anarchy, his character gradually deteriorated over time.

The main character of Sons of Anarchy Jax Teller undergoes a transformation throughout the course of the series from an enthusiastic, bright young future leader to a jaded, irate biker gang leader. Charlie Hunnam’s portrayal of Jax in the first couple of seasons won us over because of his boundless charisma and drive, fierce commitment to the people he loves, and interest in his father’s writings. Jax is a fascinating, multifaceted young man with a promising future.
But it didn’t exactly work out like that. Instead, we observe as a series of errors and tragedies gradually force Jax down a dark path until he becomes a shell of his former self. Here are five instances in which Jax Teller deteriorated during the course of Sons of Anarchy.
Obsessed with retaliation

When we first meet Jax, his commitment to everyone around him—particularly his fellow Sons and his mother, Gemma—is what drives him most. He has a moral compass that guides him as he securely negotiates the world of gangs, firearms, and violence. He is opposed to anything that may hurt them over the long run.
However, when a slew of terrible incidents alter him and the world, his allegiance is supplanted as a driving force by retaliation. For Opie, Tara, Bobby, and pretty much everyone else he has lost, he seeks retribution. Jax loses himself in the act of retaliation.
More brutal

Jax has never been opposed to violence, but his constant exposure to it has undoubtedly had an impact on him. He seemed to grimace at the extremes in the beginning of the series, and his discomfort was evident in the famed “fire or knife” moment in the first season. When he eventually gets his hands on Tara’s suspected killer, he’s not afraid to get creative with pliers, knives, and salt, unaffected by his victim’s intense suffering. However, his frequent exposure to actions like this make him become someone fearless of committing it himself. At this time, Jax Teller’s true level of violence is shown.
Added Careless

Wisdom does not always come with age. In an odd turn of events, Jax Teller’s age transforms him from a youthful, intellectual prospective leader who prefers carefully considering his plans into a violent, impetuous leader.
He becomes more and more convinced that acting on impulse and following his initial inclination is the best course of action as his power grows. Sadly, before it can be corrected, his careless actions have already done too much harm.
Place the SAMCRO concept before the SAMCRO creators

Any group, club, or organization is only as good as its members. And SAMCRO is a group of individuals who Jax Teller is meant to cherish and put before everyone and everything.
But as the show goes on, we see Jax start to hold up an ideal of what he thinks the Sons ought to be, disregarding the actual individuals that make it up. To the disadvantage of the people he should care about most, Jax becomes a poorer and worse leader as a result of prioritizing the notion of SAMCRO above his real brothers.
Put his kids in danger

We witness Jax do his hardest to be a loving parent just after Abel was born at the beginning of the season. For the first several seasons, he goes to great lengths to assure the safety of his child, including flying to Ireland to get Abel. But as the show goes on, he starts to struggle with being a good father. They are repeatedly put in danger by his continual risks and growing carelessness, which are activities that the younger Jax would never have performed. He only realizes he must send the boys away to secure their safety at the very end of the series.
Transformed into a straight villain from an anti-hero

Jax’s general character development begins with him torn between Clay, his father surrogate, and the principles of his own father. As Jax drifts more from his father’s beliefs and more into Clay’s, he is forced to walk a fine line between plainly being a criminal and not being a “bad person,” which causes him to achieve a balance in his actions. This progressive change in character makes Jax less of a likable anti-hero and makes him the show’s antagonist, responsible for many of the issues the club encounters on a daily basis. He has fully transitioned from anti-hero to villain by the time he encounters Mr. Mayhem.