The Dalai Lama is the head of the Gelug school of Tibetan Buddhism. The title "Dalai Lama" was given by Altan Khan to the then-leader of the Gelug school, Sonam Gyatso, in 1578. Sonam Gyatso became the 3rd Dalai Lama, while the first two tulkus in the lineage were posthumously awarded the title.
Since the 17th century, the Dalai Lama has been a symbol of unification of the state of Tibet and an important figure of the Gelug tradition. The current Dalai Lama, Tenzin Gyatso, escaped from Lhasa in 1959 during the Tibetan uprising and lives in exile in Dharamshala, India.
From 1642 to 1951, the Dalai Lama led the secular government of Tibet, which was known as the Ganden Phodrang. After the Qing dynasty collapsed in 1912, the 13th Dalai Lama declared Tibet's independence, though it was not formally recognized internationally.
In 1951, the 14th Dalai Lama ratified the Seventeen Point Agreement with China but revoked it in 1959. Since 2005, he has publicly agreed that Tibet is part of China and does not support separatism.
According to Tibetan Buddhist doctrine, the Dalai Lama chooses his reincarnation. The 14th Dalai Lama has emphasized that his reincarnation should not be subject to external political influence.