At first, Jack seemed to have it all together and because of that became the reluctant leader of the plane crash survivors.
Before coming to the island, Jack, a spinal surgeon, had issues with his father and his wife. Once on the island, Jack thought he saw his dead father. Jack is in love with Kate and has feelings for Juliet. He spent some time with the Others after being captured.
Jack left the island, but realized it was a mistake and worked with Ben to get all those who left back to the island.
Kate was on Flight 815 being escorted by a Marshal after being on the run for killing her father. On the island she became close to Jack and wanted to be included in everything that was going on. She also developed feelings for Sawyer.
Kate left the island with Claire's baby after Claire had disappeared. Back in the real world, she told everyone that Aaron was her child.
Kate did not want to go back to the island despite Jack telling her they had to. She finally agreed to it when she got spooked when a lawyer wanted a maternity test. Kate left Aaron with Claire's mother and returned to the island.
James Ford was eight years old when a con man stole his parents' money. His father shot his mother and then himself. The con man's name was Sawyer, so James took on the name of Sawyer. He killed a man in Australia, thinking he was the man who'd conned his parents. He was returning to the U.S. when the plane crashed on the island.
On the island, Sawyer hordes supplies, and does what he can to make everyone hate him.
When the island began skipping through time and then landed in 1974, Sawyer made up a lie and began to work for Dharma as a security guard. He and Juliet got very close and began living together. When Juliet was pulled in the Swan Station hole, Sawyer tried to save her, but he couldn't hang on.
We first knew him as Henry Gale when he was captured in Rousseau's net and then taken to the hatch by Sayid. Later, Ben and the Others captured Jack, Kate, and Sawyer and kept them prisoner. Ben seems to be the leader of the Others and is generally accepted as a bad guy, but he has had some sympathetic moments.
Locke spent his childhood in foster homes. As an adult, his mother reached out to him and made sure that he found his father, who made friends with him, only to steal his kidney.
Locke confronted his father, who pushed him out of an eight story window. With the help of the mysterious island man, Jacob, Locke survived, but was paralyzed. Locke was paralyzed until the crash. The island's healing powers healed him and Locke set out to do whatever the island wanted him to do.
Locke was transported off the island after turning the wheel and lived as Jeremy Bentham, trying to get those who had left the island to return. Ben killed him, but he showed up on the island alive, only he wasn't himself, he was Man in Locke.
His real name is Hugo Reyes, but he goes by Hurley and everyone seems to like him. Hurley believes he is cursed by the numbers 4, 8, 15, 16, 23, 42 after he used them and won the lottery. The numbers keep showing up in various places, including the hatch.
Hurley is one of the survivors who made it off the island and then went back.
Sun was a lonely housewife who wanted to get away from her husband, Jin, but ended up staying with him. On the island, Sun realized she was pregnant and Juliet did an ultrasound so that Sun would know if the baby was Jin's or the man's whom she'd had an affair with before crashing on the island. Juliet determined that the baby was Jin's and conceived on the island, which meant that Sun would die in the second trimester.
Sun was among the first to leave the island for the freighter, and then got on the helicopter. She saw the freighter blow up and believed Jin to be dead. Sun delivered her baby back in the real world, but decided to go back to the island after Ben told her Jin is alive.
Jin and his wife, Sun, were traveling together when the plane crashed. Jin did not know that his wife spoke English and had been planning on leaving him. He was an overbearing husband to begin with, but soon lightened up.
Jin was very excited to learn that his wife was pregnant and the two were among the first to travel to the freighter that was there for their rescue. There was a bomb on the freighter and they had to leave in the helicopter quickly. Jin did not make it to the helicopter and the freighter blew up. Jin survived and made it back to the island.
Sayid made it off the island and after the love of his life, Nadia was killed, he began killing people for Ben. He returned with the rest to the island and ended up in 1977. He was captured by Dharma, escaped, and shot young Ben.
Young, pregnant Claire was on her way to meet the couple who was going to adopt her baby when Flight 815 crashed. Claire became close with Charlie. The two were kidnapped and taken to the medical hatch by the Others. Alex helped Claire escape and she made it back to the 815 survivors. She soon delivered a baby boy, whom she named Aaron. Claire left Aaron when she saw her father on the island.