When he was a boy, Ben was shown to be polite and innocent. He was unhappy with his father and dreamed of joining the Others. When Richard cured him, Ben seemingly “lost his innocence.”
As an adult and the leader of the Others, Ben acted as a main antagonist for a long part of the series. He is an expert liar: he can easily bring anyone to do what he wants, finding the perfect arguments. Incredibly calculating, Ben always has a plan to achieve his aims and rarely fails. He doesn’t mind killing anyone on his way, but does so only when he needs to.
Ben is eloquent, calm and shows few emotions. When he does, he is very different. He is easily angered when the few things he truly cares for (his adoptive daughter Alex, Juliet, and his leadership of The Others) are threatened. Being used to be handling all situations in his favor, Ben is upset when someone else tells him what to do.
When compared to his usual state, Ben can be quite childish when his emotions do bleed through. He maintained an infantile crush on Juliet, his obsession with her having disasterous consequences in the forms of Goodwin's death, Juliet's betrayal and defection to the survivors, and the ruining of Ben's plans to solve the pregnancy issues that plagued the Others. Ben also has issues letting go of a grudge, as he utterly refused help from Charles Widmore to prevent the Man in Blacks's escape, going so far as to switch sides and murder Widmore, proving just how long Ben can be willing to hold on to hate. Ben becomes jealous quite easily, as shown at two important times: Goodwin's death, and Jacob's murder. Ben despised Goodwin's relationship with Juliet, and arranged his death as a result. Jacob's death is the more signifigant incident, as Ben shows when all he asks Jacob is why he was rejected in favor of Richard and "Locke", saying "What about me?", becoming homicidally enraged by Jacob's calm attitude and simple answer: "What about you?" and stabbing Jacob on the spot in a temper tantrum, instantly regretting his actions when he realizes the implications of his actions.
After meeting the Man in Black and killing Jacob, Ben seems to lose his confidence. At this point he has lost everything important to him: his "daughter" Alex, whom he truly loved; and what he has always fought for, his leadership. He seems to feel that all he can do is follow the survivors to stop the Man in Black from leaving the Island. He seemingly starts to feel remorse for the crimes he has committed.
Ben, despite his memories of his life on the Island being restored via physical assault by Desmond decided not to "move on", deciding to pursue "other things" in the sideways timeline, likely a relationship with Alex and Danielle. Sitting outside the church as the Flight 815 survivors waited, he had talked to John Locke about what he done on the Island to Locke, and for killing him. He did all those things to him because he knew that Locke was special and he wasn't. He admited that he was selfish and jealous of Locke's specialness. Locke told him sincerely that he forgave him. Ben was visibly moved, voice trembling he told Locke that his forgiveness meant to him more than he possibly could know. As Locke rolled away Ben suggested that he really didn't really need that wheelchair. At that Locke stood up, looked at Ben triumphantly and walked into the church. While admitting Locke, Hugo Reyes saw Ben and invited him in. Ben declined. Ben in reference of his caretakership of the Island succeeding Jack Shepherd, called him the best No.1. Hugo in turn called Ben the best No.2. hinting at a long relationship together as caretakers of the Island that was much more harmonious than what was between Jacob and The Man In Black. At that Hugo went into the Church to "move on" with the other 815 survivors and Desmond, Penny and Juliet. Ben stayed to probably continue his "life" with Danielle and Alex.