The "others" as the main characters refer to them or the "hostiles" as the members of the dharma initiative call them are a group of people that inhabit the island long before anyone else arrived. There reason for being their is shrouded in mystery and they seem to have some communion with the island to the point of worshiping it as a sacred place. They believe the island will watch over them if they follow certain rules which come up as the show progresses. In the beginning of the show they come off as uneducated savages living in wood huts but it is later revealed that they only act that way to fool new comers and they are actually a very advanced people. Due to an event that happened on the island long ago they are unable to have children so they take the children and pregnant woman of every group that becomes stranded on the island.
*WARNING - THE FOLLOWING INFORMATION MAY CONTAIN SPOILERS IF YOU ARE NOT CAUGHT UP IN THE SHOW.
Benjamin Linus - The Leader of the others during the time of the plane crash. Although the other leaders have had to follow certain rules Ben has had no problem breaking them, as well as lying and manipulating everyone around him to protect himself and get what he wants. Many of his people question his leadership ability but they follow him because that's what the rules say they must do.
Richard Alport - Richard is the second in command of the others, although he seems to know more about the island and everything that goes on than any of the leaders ever have. He was once leader himself but had to give it up for unexplained reasons. Richard has appeared in many flashbacks of different characters past but in all of them he always appears to be the same age, even as far back as 50 years before the shows present, the reason for this is unknown and has led to much speculation over his character.
Tom "Mr. Friendly" - Tom was the other that all the main characters believed was in charge for the first 2 seasons of the show. He was nicknamed Mr.. friendly by the shows fans because although every time he appeared he said or did something sinister he always had a big smile on his face and appeared to be non threatening. After it was revealed he was not actually the leader his whole demeanor changed in the following seasons, he was revealed to be gay and a very sensitive guy.
Juliet Burke - Juliet was a fertility doctor that was recruited by the others to come to the island and help discover why the woman couldn't have babies. After years of failure she wanted to give up and return to the mainland but Ben would not let her leave. She later helped Jack and the other survivors by betraying the others and joined the castaways.
Ethan Rom - Ethan was the doctor of the others before the plane crash, after that he was ordered to infiltrate their camp and pretend to be a plane crash survivor like the others. Eventually his alias was found to be false and they discovered he was never on the plane, but by that time he had determined who the pregnant woman were, claire being the only one and kidnapped her to take her baby. Eventually Claire escaped and when he came back looking for her he was killed by charlie.
Goodwin Stranhope - Goodwin was Juliets love interest in the years prior to the plane crash (although he was married which made their relationship an affair). Just as Ethan was ordered to infiltrate the survivors from the front end of the plane, Goodwin was ordered the same but of the tail section survivors. Eventually he was discovered to not have been on the plane and was subsequently killed by Ana - Lucia.
Mikhail Bakunin - Mikhail was a Russian soldier who after the cold war was recruited by the others. His job was to guard the dharma station known as the flame and monitor activity from the outside world. When the plane crashed he researched detailed background checks on each of the survivors to learn everything about them and determine if any of them would be useful.