Charles Widmore
Season five's "Namaste" shows a young Ben coming into contact with a captured Sayid Jarrah (Naveen Andrews), who along with several other Oceanic Flight 815 survivors has been brought back in time from 2007. In the following episode, "He's Our You", he helps free Sayid under the impression Sayid was sent by the Others to bring him to Richard. Sayid instead shoots Ben and leaves him for dead. Fellow crash survivor Jack Shephard (Matthew Fox) refuses to help the boy, so Kate Austen (Evangeline Lilly) and James "Sawyer" Ford (Josh Holloway) take Ben to Richard, who informs them Ben will henceforth lose his innocence and always be one of the Others. In 1987 (or possibly 1992) he assists the hostiles in using poisonous gas to kill the Dharma Initiative, including his father. In 1988, Charles Widmore, leader of the Others, sends Ben to kill French scientist Danielle Rousseau (Melissa Farman), who was marooned on the island. However, when Ben learns Rousseau has a child, he kidnaps the baby Alex Rousseau, warning Rousseau to never come looking for the baby if she wants either of them to live. He banishes Charles Widmore from the island and assumes his leadership role, as he is the only one who can allegedly interact with their real leader, Jacob, and communicate his will to the group.