Dharma Initiative
The Others are a group of inhabitants that have been on the island for an unknown number of years. It is known that their occupation precedes both the Dharma Initiative and the U.S. Army's exploration of the island; as well as the survivors of Flight 815. Early flashbacks show they have been on the island since at least the mid-19th century, and both Jacob and his rival existing on the Island for time preceding even that (definitely hundreds, possibly thousands of years). The Others used to reside in the barracks first built by the Dharma Initiative to house their employees, after the Purge, but have left the Barracks during season 3 and have not returned.