Since Then: Charlie, who'd long wanted to take care of a family, tried to help raise Aaron while on the island. Claire originally accepted this arrangement, and Charlie even helped retrieve Aaron after a kidnapping. Claire later pointed out that Charlie was not his father, and Charlie ended up kidnapping Aaron himself, convinced he had to baptize him. Before he died, Charlie left Aaron his heirloom ring. In his aferlife, Charlie again witnessed Aaron's birth and woke up soon after.
Origin: Charlie and Claire developed a bond throughout most of the first season, as Charlie reached out to Claire as a friend.
Since Then: However, as Claire starts to trust Charlie and lean on him, she is kidnapped by Ethan who also attempts to murder Charlie by hanging him from a large banyan tree. When Claire returns she does not remember the events or the people she has met since the day of the crash. Charlie reaches out to her again to gain her trust back. After Aaron is born, Charlie voluntarily assumes the role of 'daddy' to Claire's 'mommy', a bit to Claire's surprise. But when Claire discovers Charlie is/was a heroin addict, she gets angry at for lying to her and the situation only grows worse when Charlie, prompted by dreams that he interprets as prophecies, tries to kidnap Aaron to baptize him in the ocean. After this incident, Locke decides to watch over Claire while Charlie looks on jealously. Things seem to be on a standstill for a while until Charlie returns from the the Swan Station discharge, and Claire looks genuinely happy to see him alive and well. That evening, she kisses him. However, once Charlie discovers that Desmond's clairvoyant flashes all revolve around his own death, he volunteers himself to swim down to the Looking Glass station to un-jam incoming transmissions. Realizing his doomed fate, he says goodbye to Claire but doesn't tell her that he doesn't plan to return. During his heroic act, he drowns. Claire is devastated upon hearing of Charlie's death.
Since Then: Desmond's mind traveled back in time and saw Charlie performing on a London street corner. He began experiencing premonitions of Charlie dying and repeatedly saved his life. He was present when Charlie died. In the afterlife, Charlie helped guide Desmond toward awakening.
Origin: Eko learned Charlie carried a Virgin Mary statue and demanded he lead him to where he'd found it.
Since Then: Charlie began following Eko, inspired by his faith. He asked Eko about baptizing Aaron and helped Eko build a church. When Locke and Desmond locked themselves in the Swan, Charlie fetched dynamite, and the two together tried to blast their way in. Charlie later helped Locke save Eko from a Polar bear.
Origin: Ethan kidnapped Claire & Charlie while Claire was having false contractions.
Prize: Aaron. Because he was pressured to kidnap Claire and her baby for the Others, Ethan wanted Aaron badly enough to cut him out of Claire early, and Charlie wants to protect both Aaron and Claire.
Fuel: Ethan kidnapped Charlie and Claire when they were alone in the jungle ("Raised by Another"). To distract his pursuers, Ethan hanged Charlie hanged from a tree ("All the Best Cowboys Have Daddy Issues"). Ethan then took Claire to the Staff and (presumably) drugged her repeatedly, giving her sour water and injecting her pregnant belly. Eventually Claire escaped, but had no memory of anything since the crash- including the time she'd spent with Charlie. When Ethan found out that Claire was missing, he demanded that she be returned to him. He killed Scott when Claire wasn't returned before the deadline. Using Claire as bait, the Losties set a trap for Ethan, and captured him ("Homecoming").
Since Then: The pair's first major scene together was when Charlie solicited Hurley's help in catching fish for Shannon. Later, Hurley built a golf course, and the two danced to distract other players. Claire got attacked shortly after, and Charlie heard the news from Hurley. Some days later, Charlie followed Hurley to Danielle' shack, and the two crossed a rope bridge together. When Hurley assumed control of the Swan pantry, Charlie asked him for a jar of peanut butter, and Hurley eventually complied. He also told Charlie about his lottery win, though Charlie didn't believe him. Hurley later asked Charlie about Libby. After the Swan implosion, Hurley and Charlie stumbled upon Desmond, and the two soon discussed Desmond's apparent powers. The two eventually got Desmond drunk to discover the truth about them. To avert Charlie's fate and Hurley's curse, the two started the DHARMA van. The two later went on a mission with Desmond and discovered Naomi. Charlie eventually came to terms with his imminent death, refused to let Hurley follow him to the Looking Glass and hugged him goodbye. Hurley shared the news of Charlie's death with Claire, crying, and consequently decided to join Locke's camp. Once Hurley returned to the mainland and checked himself into Santa Rosa, Charlie's ghost visited him repeatedly, urging him to return to the island and relaying a message from Christian. After Hurley died and woke up, he saw Charlie again and kidnapped him, taking him to the concert so he could wake too.
Origin: Charlie accompanied Kate to the cockpit, hoping to retrieve his heroin. She told him she was happy he came.
Since Then: The two shortly after went on another mission to find a radio signal. Later, after Charlie was kidnapped, Kate searched for him with Jack and witnessed his resuscitation.
The two interacted rarely after this, but Charlie's work in the Looking Glass let Kate find rescue and spend years in Los Angeles, raising Aaron, Charlie's surrogate son, as her own. After death, Kate thanked him for his sacrifice and helped him remember his life.
Origin: Locke's mistrust of Charlie over heroin addiction.
Prize: They both believe that they are fighting for Claire and Aaron's best interests.
Fuel: Locke found Charlie's new heroin stash after he had tried to help him kick his addiction and punched him out when Charlie tried to baptize Aaron ("Fire + Water"). Charlie thought that Locke was trying to steal his role as a father figure for Aaron, after Claire kicked Charlie out ("The 23rd Psalm"). Charlie's consequently participated in Sawyer's con to make Locke look foolish ("The Long Con") and also helped Eko break into the Swan after Locke initiated a lockdown ("Live Together, Die Alone, Part 1").
Resolved: Apparently resolved. After the Discharge, Locke seemed willing to set old hurts aside, and even asked Charlie to help him by acting as lookout while Locke was in the sweat lodge. With Locke acknowledging and taking responsibility for his own shortcomings, Charlie seems to no longer carry a grudge. Shortly afterward, Charlie died, thus ending this rivalry.
Since Then: Charlie targets Lucy Heatherton, a rich British woman from Knightsbridge, in order to steal money for heroin. Lucy's father owns a rich corporation, which enables him and his daughter to live in comfort in a big house, with lots of precious artifacts and interesting ornaments. Lucy's father gets him a job at his company selling photocopiers. His first day of work finds him going through heroin withdrawals and he steals a valuable cigarette case, previously belonging to Winston Churchill, from his Lucy's house. Without any time to buy his drugs and get a fix, Charlie miserably fails at his job and loses his Lucy as a result of her discovering his attempted con of her and her father.
Origin: Charlie accompanied Sayid on his early expedition to get a signal on his radio
Since Then: When Rousseau kidnapped Aaron, Charlie blamed Sayid and hit him. Sayid didn't fight back but just warned him against trying again. The two together tracked Rousseau and retrieved the baby. Some weeks later, Sayid interrogated an Other, and he told Charlie he did this because he remembered what Ethan did to him and Claire. The two together followed the prisoners' map to Henry Gale's balloon. Later, when Charlie and others discovered Naomi, he decided to trust Sayid with the news.