The following article written by the International Buddhism Sangha Association is taken from the book H.H. Dorje Chang Buddha III:
In our world, Buddhism can be divided into Hinayana, Mahayana, and Vajrayana based upon the differing aspirations behind cultivation as well as the magnitude and speed of accomplishment in the dharma. Further divisions can be made based upon sects or schools. Tibetan esoteric Buddhism can be divided into twelve sects, such as Nyingma, Kagyu, Sakya, Geluk, and Jonang sects. There are also many branch sects. Within Buddhism there is also esoteric Buddhism taught by Sakyamuni Buddha contained in the Tripitaka, the Shingon sect, and exoteric Buddhism, which includes Zen Buddhism, the Pure Land school, and the Vinaya school, and many other schools.
However, whether it is Hinayana, Mahayana, Vajrayana, or any of the aforementioned sects or schools, they have all received their lineage from Dorje Chang Buddha. With respect to all of Buddhism in the dharma realm, Dorje Chang Buddha is the true primordial ancestor with form. Without Dorje Chang Buddha, there would be no Buddhism, no Buddha-dharma, no Buddhist studies, no Buddhas, no Bodhisattvas, no dharma kings, no rinpoches, no dharma teachers, and no Buddhists. There would only be the concept of the absolute truth of the universe that is not born and does not perish. This is the formless dharmakaya Buddha known as Samantabhadra Tathagata or Adharma Buddha. The dharmakaya has no form. It has no sound and does not speak. This dhamakaya is called Buddha-nature, which is not Buddhism. It abides in perfect stillness. With the dharmakaya, there is no subject who can expound the dharma.
The dharmakaya of Samantabhadra Tathagata generated the sambhogakaya Dorje Chang Buddha with form. Dorje Chang Buddha originated Buddhism in the dharmadhatu and began to spread the teachings of Buddhism in the three spheres of existence. Dorje Chang Buddha has come to this world twice. The first time was in the form of the holy and venerable Vimalakirti, who was Dorje Chang Buddha II. The second time was in the form of H.H. Wan Ko Yeshe Norbu, who is Dorje Chang Buddha III. The original leader of all of the sects within all of Buddhism, whether esoteric or exoteric, is Dorje Chang Buddha.
]No matter what Buddha-dharma it may be, it was originally transmitted by Dorje Chang Buddha because Dorje Chang Buddha is the only primordial ancestor of Buddhism. Dorje Chang Buddha transformed into the ancient Buddha Dipankara, Vajrasattva, and others. The ancient Buddha Dipankara taught dharma to Sakyamuni Buddha. Sakyamuni Buddha was the first to teach the dharma in the earthly realm. However, the source of all Buddha-dharma is the original ancestor of Buddhism, Dorje Chang Buddha. If you cross-reference the names and numbers on the list with the numbers on the lineage refuge tree [as shown in the treasure book H.H. Dorje Chang Buddha III], you will have a rough understanding of this. Thus, the three primordial Buddhas in the dharmadhatu are called dharmakaya-Buddha Samantabhadra Tathagata (Adi Buddha aka Adharma Buddha), sambhogakaya-Buddha Dorje Chang Buddha (Buddha Vajradhara), and the nirmanakaya Vajrasattva.
For more than two thousand years, different Buddhist sects have mixed together and have originated from one another. Patriarchs have taught dharma to one another and have learned from one another during these more than two thousand years. This has caused the network of lineages within all of Buddhism to become extremely large and complex. Such a lineage refuge tree surely cannot be clearly depicted in just a few pages. Because of space limitations, it was not possible to include in this lineage refuge tree all of the Buddhist sects, all of the Buddhas and Bodhisattvas, and all of the great patriarchs. Thus, this lineage refuge tree only includes a few percent of them in a representative capacity. Nonetheless, everything stated above regarding lineages is accurate and unbiased.