The Dalai Lama is the leader of the Gelug sect of Tibetan Buddhism. The current and 14th Dalai Lama is Tenzin Gyatso. Every other Buddhist sect in Tibet recognises the Dalai Lama as the religious and political leader of all Tibet. In fact, the Panchen Lama has a higher religious status than the Dalai Lama, and thus the Dalai Lama is more the temporal head of the Gelug. This position effectively made him ruler of Tibet and Head of State during the period when the Gelugpa controlled the country (the mid-17th century until 1959, when the Dalai Lama had to flee to India).
Dalai means "Ocean" in Mongolian and "Lama" is Tibetan for high reincarnation, it is commonly referred to "Ocean of Wisdom", a title bestowed by the Mongolian ruler Altan Khan upon the 3rd Dalai Lama and now applied to every incarnation in the lineage. The Dalai Lamas are believed to be manifestations of Avalokiteshvara, the Bodhisattva of Compassion, whose name is Chenrezig in Tibetan. Bodhisattvas are enlightened beings who have postponed their own nirvana and chosen to take rebirth to serve humanity.
The Tibetans name the Dalai Lama Gyawa Rinpoche meaning great protector, or Yeshe Norbu meaning the joy fulfilling jewel.
Upon the death of the Dalai Lama, his monks institute a search for the Lama's reincarnation, or tulku, who is usually a small child. Familiarity with the possessions of the previous Dalai Lama is considered the main sign of the reincarnation. The search for the reincarnation typically requires a few years which results in a gap in the list of the Dalai Lamas. The reincarnation is then brought to a monastery to be trained by the other Lamas. The process is not always peaceful; at times rival groups of lamas each "discover" a child and claim it is the true reincarnation. This has historically turned into political struggle to decide who is the real Dalai Lama, in a manner analogous with the Pope and the Antipope stories in the Christian world.
The government of the People's Republic of China has asserted the power to approve the naming of high lamas in Tibet and has exercised this power in the naming of the Panchen Lama, who is empowered to recognize the new Dalai Lama. Many observers believe that with the death of the current Dalai Lama, the PRC will direct the selection of a successor thereby creating a schism and leadership vacuum in the Tibetan independence movement.
As the most powerful figure in the Gelugpa or Gelug sect of Tibetan Buddhism, the Dalai Lama has received the highest teachings and empowerments of all the main schools of Tibetan Buddhism. He also presents core teachings from all of these main schools. Until the 14th Dalai Lama's exile in 1959, the Dalai Lamas resided in the Potala Palace during winter and in the Norbulingka residence during summer, in Lhasa.