In season one it was said in Jack's flashback that his wife was a crash victim he operated on. Here I lifted this from Wikpedia, it helps explain his wife and a recap on the character for you:
Prior to Oceanic Flight 815
Jack is a neurosurgeon who lived in the United States. He traveled to Sydney to find his missing father, Dr. Christian Shephard.
Apparently early in his medical career, he operated on a car crash victim named Sarah. He was forced to perform surgery, but seemingly failed and told her her back was broken. However, she was able to move her toes and feel in her legs, so she could walk again. They eventually married, although by the time of the flight, he is unmarried and no longer wears his ring.
Christian had operated on a woman while under the influence of alcohol; when Jack discovered this he relieved his father of the surgery. He was unable to repair the damage, however, and the woman died. Christian pressured Jack to sign a report saying the woman was beyond medical assistance, but during the inquiry Jack discovered the woman was pregnant and revealed the truth. His father fled with his medical career shattered, eventually ending up in Sydney. While there, Christian encountered Sawyer in a bar and told him that he wanted to apologize and tell his son that he did the right thing, but was too weak to call him. Christian Shephard later died of alcohol poisoning. When Jack left the United States, he knew only that his father was missing. Eventually he found him, in a Sydney morgue. Jack had trouble getting the casket onto the plane but was eventually successful.
On the plane, he was seated next to Rose. When the turbulence struck, Rose's husband was in the bathroom and Jack promised to take care of her until he returned. Before the plane's tail section broke off, Jack fell unconscious.
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On the island
At the beginning of "Pilot: Part 1", we see that Jack was thrown into the woods and had multiple gashes, including a large one on his back. Upon finding the plane's wreckage on the beach, he tends to many survivors but is unable to save all of them. He enlists Kate to sew the gash on his back, marking the beginning of their friendship. He leads an expedition with Kate and Charlie to find the cockpit and the plane's transciever. Together they find it but also witness the pilot's death at the hands of the "monster".
Jack is quickly thrust into a leadership role by the other survivors because of his medical training and take-charge attitude. He quickly develops a rivalry with Sawyer, mainly over Kate and her feelings towards them. Starting in "Walkabout" and continuing in "White Rabbit", Jack begins glimpsing his father distantly. He chases the image, which eventually leads him to a cave shelter and source of fresh water. He also finds his father's casket, empty. Jack gets some of the survivors to join him in the caves, while others remain on the beach, hoping to spot a rescue ship.
Until "All the Best Cowboys Have Daddy Issues", Jack is mainly seen performing medical duties, such as trying to help Shannon with her asthma, or Claire with her false labor pains. In that episode, he hastily tries to find Ethan after he abducts Charlie and Claire. When they find Charlie, Jack attempts to save him with CPR, but to little avail at first. Even when Kate tells him to give up, Jack continues until he resuscitates Charlie.
When Kate tries to get a case that was the U.S. Marshal's, she gets Jack to help exhume the Marshal's body to find the key. After Jack finds the guns in the case, he takes it and the key and hides it. He first takes them out when he, Sawyer, Charlie and Sayid decide to trap Ethan. In "Deus Ex Machina" and "Do No Harm", Jack works furiously to save Boone, who had suffered fatal injuries in the previous episode. However, he finds himself still having trouble letting go, a problem we have seen foreshadowed in most of his flashbacks. Boone eventually tells Jack to let him go, to which Jack agrees. Since then, Jack's distrust of Locke has grown due to Locke not telling Jack everything that's going on.
In "Exodus", Jack is part of the team that retrives the dynamite at the "Black Rock" and that plans to open the mysterious hatch. Before he leaves, he and Sawyer make up when Sawyer tells him about the encounter he had with his father. Jack and Locke put aside their differences in order to open it, although Locke says that the reason they don't get along is because Jack is a "man of science," while Locke is a "man of faith."
I missed it last WED cause I was still watching the first season DVD's and didnt want to screw-up the storyline.
