Dr. Jack Shephard was a spinal surgeon and the survivors’ de facto leader. Before the crash, his obsessive personality wrecked his marriage and his relationship with his father. On the Island though, the survivors sought his guidance during many crises and missions, and he united them until they cooperated and formed a society.
Jack developed romantic relationships with Kate and later Juliet, and his jealousy sparked a rivalry with Sawyer. His rationality, so useful when solving problems, prevented his accepting the Island’s mystic properties and caused friction with “man of faith” John Locke. Problems arose that Jack could not fix despite his obsession and self-sacrifice. Though he tried to repress his guilt, he often broke out with violence or tears.
After suffering a kidnapping and almost negotiating his own rescue, Jack escaped the Island with five other survivors. Off-island, he laid his father to rest and proposed to Kate, but visits from John Locke and his father’s ghost sent him toward depression and substance abuse. Yet he gained new faith, and he led the survivors back to the island, believing it was his destiny. He then found himself in the past, where he tried to reset his and the others’ lives and prevent the crash of Oceanic 815.
The attempt failed, sending Jack to a new low. But after discovering he was a candidate to replace Jacob as Protector of the island, he gained confidence and decided to stay on the island. He also ceded decision-making to Sawyer, overcoming his control issues. He chose to become the Island’s new protector and was almost killed by the Man in Black, but with Kate’s help, he killed him before he could leave. He then sacrificed himself to relight the Heart, saving the Island from destruction. Post-death, he imagined a son and an ex-wife to come to terms with his bad relationships. His personality mixed science and faith, but he again felt the compulsion to fix others. His stubbornness returned, and unlike his friends, he resisted remembering his life, even after experiencing flashes. Eventually though, he remembered everything and after seeing his father again, he was able to “let go”, reuniting with Kate and his friends, to finally move on in the church.