The Dalai Lama is believed to be the rebirth of a long line of tulkus, who have chosen to be reborn in order to enlighten others. He is also the official leader of the Tibetan government-in-exile, or Central Tibetan Administration (CTA). Between the 17th century and 1959, the lines of Dalai Lamas were the head of the Tibetan Government, administering a large portion of the area from the capital Lhasa, although the extent of the lineage's political authority and rulership over territory has been contested. Since 1959, the Dalai Lama has presided over the former government of Tibet, now a government in exile. The Dalai Lama is often thought to be the head of the Gelug School, but this position officially belongs to the Ganden Tripa, which is a temporary position appointed by the Dalai Lama (who in practice exerts more influence).