Old Tibet was rigidly stratified: the highest rank was Buddhist lamas, the next were nobles and the lowest were serfs and slaves. Government officials were lamas and nobles who made up the ruling class, while serfs and slaves, as the class to be ruled had no political status.
The Dalai Lama is the top leader in both religious and people's world, who grasped the powers of religion and administration. He is the most senior living Buddha in Tibet. His position was passed down through reincarnation, not hereditary system.
The Dalai Lama can be from an aristocratic family, or a common farmer's family. The present 14th Dalai Lama was from a farmer's family in Qinghai Province. According to the old Tibetan system, the holder of the post of Dalai Lama became the highest noble in Tibet overnight, even if he was born to a poor family. The Dalai Lama represents the interest of nobles, not that of poor people.
According to Tibetan practice, the Dalai Lama can not take over the reins himself until he is 18 years old. Before the Dalai Lama takes the reins, the power is held by the Prince Regents. And only the Living Buddhas were in a position to serve as Prince Regent.
It is not difficult to find that the Dalai Lama as well as Prince Regent were far beyond religious roles. They developed their political career in the name of Buddhism.