The Others are a group of Armageddon Waiters, people who had set up bunkers / communities during the Cold War on these remote islands to await nuclear armageddon, and to survive it if possible. Unrelated to them, the Hanso Foundation / Dharma Initiative had also set up shop on these islands to conduct their experiments which revolve around the strength of Good and Evil, namely which of these is stronger in people. The Dharma scientists, after stumbling upon the Armageddon Waiters, decided to do some experiments on them, but these got out of control and the subjects eventually revolted and took everything over. The nature of the Dharma experiments involved harnessing negative psychic energy from people, which is what the Monster is, and which is why the Others seem so aggressive. This opened up some latent psychic powers in some of them which allow them to prophesy and manipulate minds to some extent.