LOST Survivors: Jack Shephard

Season One:
At the end of season one (don't read this if you don't want to know any spoilerific information), this is what we know about Dr. Jack Shephard (Matthew Fox).

Jack has always had a rough relationship with his father Christian Shephard. He felt like he would never be good enough for his father. Jack is a spinal surgeon. Jack married a patient that he fixed, named Sarah.

Jack reported his father for being under the influence during a surgery that led to a pregnant woman's death. Christian was subsequent fired and spiraled out of control leaving the country. Jack's mother sent him to Australia to find his father. When Jack arrived he learned that his alcoholic father had died. Jack identified him in the Sydney morgue and was taking his body back to LA for the funeral.

Since crashing on the island, Jack, the only doctor among the survivors, quickly became a leader in the camp. Thanks to visions of his dead father, Jack discover the caves and the fresh water there, and was able to get the survivors to move inland. Interestingly enough, the people with life threatening injuries Dr. Jack was unable to help them.

He helped the get the dynamite to blow open the hatch planning on hiding everyone in there to escape the Others.