Jack Shephard (Matthew Fox) was a spinal surgeon before the crash of Oceanic Flight 815 stranded him on the island in "Lost." He was returning from Syndey to retrieve his father's body for burial when the plane crashed. His relationship with his father, Christian (John Terry) had been strained at the time because Christian blamed Jack for the loss of his medical license. Christian's problem with alcohol and the resulting death of a patient was the real reason for the loss of his license. Jack was also recovering from his failed marriage to Sarah (Julie Bowen), a former patient.
During his time on the island, Jack and another survivor, Sawyer (Josh Holloway) began to fall in love with Kate Austen (Evangeline Lilly). While on the island, Jack sees visions of his dead father and follows him. He finds his dad's casket empty but in his search locates a set of caves with fresh water. Jack's relationship with Sawyer continues to be antagonistic. He lets Sayid Jarrah (Naveen Andrews) torture Sawyer because he believed that Sawyer had an asthma inhaler that belonged to another survivor. Jack also withheld medicine from Sawyer after he had been shot. Sawyer ended up taking all the medical supplies and Jack had to win them back in a game of poker.
The survivors captured the leader of the "Others", Ben Linus, who was posing as Henry Gale. After Michael Dawson (Harold Perrineau) made a deal and helped Ben escape, Jack, Kate and Sawyer set out on foot to find them. They were were attacked by the Others with stun darts and taken back to their facility. They woke up as hooded prisoners with Jack held in an unused aquarium guarded by Juliet Burke (Elizabeth Mitchell), who he would later become romantically involved with. Jack makes a deal with Ben and uses his medical skills to remove a tumor from his spine. Juliet wanted Jack to kill Ben during the surgery but Kate begged him not to in order to save Sawyer.
Jack was finally able to leave the island with Kate, Claire Littleton's (Emilie de Ravin) baby, and several other survivors. Jack and Kate got engaged and decided to raise Claire's baby as their own. While Jack was off the island he found out that Claire was his half sister. He becomes convinced they have to go back to the island but when they arrive the year is 1977. After going through a time warp to get to 2007, Jack and the other survivors plan and carry out a bombing of the Swan site to stop dangerous gasses from leaking. Jack is shot while trying to detonate a bomb but is not seriously injured
"We have to go back, Kate! We have to go back to the island!"
"If we can't live together, we're going to die alone."
"There are no shortcuts. No do-overs. What happened, happened. Trust me. I know. All of this matters."
"Everybody wants me to be a leader until I make a decision that they don't like."