Youth of Inconceivable Sublime Light

The main teaching of the original teacher Buddha Samantabhadra is Dzogchen, the Great Perfection. The teachings of Dzogchen are the pinnacle of all nine vehicles. Before the Dzogchen teachings arrived in our human world, they were propagated through the Gyalwa Gong-gyü, the mind transmission of the victorious ones, in the three divine realms: first in Akanishtha, then in Tushita, and lastly in the Realm of the 33 Gods, the world of Indra and his 32 vassal kings located on the summit of Mount Sumeru.
Generally, it is said that the 6,400,000 Dzogchen teachings entered this world via Garab Dorje, the first human vidyadhara, who directly received the transmission from the Buddha in the form of Vajrasattva. These teachings first arrived in Uddiyana, and later were propagated in India and Tibet. Before the era of Buddha Shakyamuni the Dzogchen teachings were propagated in our part of the universe by other buddhas known as the Twelve Dzogchen Teachers. Buddha Shakyamuni is usually counted as the fourth guide in this Excellent Aeon in which one thousand fully enlightened buddhas are to appear in our world. Although in this context he is known as the fourth guide, Shakyamuni is the twelfth in the line of Dzogchen teachers.
No Dzogchen teachings have occurred apart from the appearance of a buddha in this world, so we must count Buddha Shakyamuni as one of the chief teachers through whom the teachings were transmitted. He did, indeed, convey Dzogchen teachings, though not in the conventional manner. His conventional teachings were primarily received by those who had a karmic connection with the teachings appropriate to shravakas, pratyekabuddhas and bodhisattvas. It was not that they were not allowed to receive the Dzogchen teachings; their karmic fortune was such that they received the teachings to which they were suited. The Buddha gave Dzogchen teachings, as well as other Vajrayana instructions, by first manifesting the mandala of a deity and then imparting the tantric teachings to a retinue seated within that setting. This, however, does not lie within the scope of what was perceived by ordinary people.
--Tulku Urgyen Rinpoche

The Tangkha is depicting Youth of Inconceivable Sublime Light (khye’u snang dam pa bsam gyis mi khyab pa) one of the first of these Twelve Dzogchen Buddhas. Shakyamuni is the Twelfth. The painting was supervised by Nyoshul Khen Rinpoche shortly before his passing.