What is the origin of the Dzogchen lineage?

The original Dzogchen lineage was transmitted from Dharmakaya Buddha Samantabhadra to Sambhogakaya Buddha Vajrasattva to Nirmanakaya Buddha Shakyamuni.

In 626 B.C.E. (2,627 years ago), our Supreme Teacher Shakyamuni was born in northern India, which is now part of southern Nepal. At the age of thirty-five, Shakyamuni attained Buddhahood in Bodhgaya, India and began to teach the dharma in this world. For the next forty-seven years the Buddha's teachings flourished throughout the universe and as a result many sentient being attained enlightenment. At the age of eighty-two, Buddha Shakyamuni passed into nirvana. Thereafter, the Buddha Shakyamuni manifested in two wisdom emanations.

Source

http://www.dzogchenlineage.org/faq.html