Ana Lucia Cortez was a survivor of Oceanic Flight 815 and an ex-police officer who had deep-seated emotional issues, due mainly to a shooting which killed her unborn child and resulted in her distrust of people and difficulty in emotionally relating to others. She also exhibited a tendency towards violence. She turned to revenge, and killed her attacker while on duty. She went to Australia on a whim with a man after she resigned from the LAPD. She realized her emotional isolation during her time with the self-destructive Christian Shepherd and booked a seat on Oceanic Flight 815. She sat in the tail section of Flight 815 when it crashed, and became the leader of the tail section survivors. Ana Lucia and the rest of the tail section survivors were torn by trust issues after they were attacked a number of times by the Others and realized that their group had been infiltrated by a spy. Nevertheless Ana Lucia discovered and killed the spy. After Michael, Jin, and Sawyer washed up on shore after their raft was destroyed by the Others, she and her group captured and questioned them and ultimately determined that their story was true. Along with Mr. Eko, she led her party across the Island to reunite them with the rest of the passengers. After Cindy disappeared en route, they were surrounded by whispers and in the confusion, Ana Lucia shot and killed Shannon, mistaking her for an Other. This incident made it difficult for her to be accepted by the group, but she was eventually welcomed and she developed a camaraderie with Jack, as well as Sawyer, after initially butting heads. While guarding Ben, she was attacked by him during questioning, and when she later went to kill him she found she couldn’t pull the trigger.
Later, Michael made a deal with the Others to help free Linus, and Ana Lucia unwittingly handed him the gun which he murdered her with in cold blood.
In the flash-sideways, she helped Desmond, Sayid and Kate all escape from prison in exchange for money offered by Hugo Reyes. Desmond said that Ana Lucia was not ready to move on with them yet.