Jack is a neurosurgeon from the USA. In the immediate aftermath of the plane crash he is the first to react to the crisis - overcoming his own pain to rescue the wounded.
With his inner strength and sharp brain he quickly emerges as a leader to the survivors, who increasingly look to him for guidance.
Jack's closest ally is Kate, but their intimate friendship sparks a rivalry with Sawyer, who seems convinced she harbours a guilty secret.
And why did Jack have such a ready and convenient supply of alcohol to sterilise the crash wounds on his back? Perhaps the good doctor has some skeletons in his own closet.