The shepherd symbolizes the leader of a flock.  The one responsible for the flock.  Most Christians believe the term "The Good Shepherd" was started by Christians and started with Jesus telling the parable of the Good Shepherd.  In truth, the Good Shepherd was a common religious symbol in many ancient religions and cultures including the Sumerians, Iranians, Orphic (Greek), Hermetic, Tibetan, and Pathagorean.  In Buddhist Tibetan tradition, the All-merciful Good Shepherd is incarnated in the Dalai Lama.  In ancient Egypt, Ra was the "Shepherd of all Men".  In Islam, "the divine glory is among the shepherds".  The ancient gods Pan and Hermes were shepherds.  In Hindu, Siva is a herdsman.  In ancient Iranian, Yima was the Good Shepherd who possessed the solar eye that holds the secrets of immortality.  Early Sumerian writings talk of the shepherd god Dumuzid and the shepherd king Etana.  In some ancient cultures, part of the oath a king took when he was crowned was to be the shepherd of the people.