Vairocana (also Mahāvairocana, Sanskrit: वैरोचन) is a celestial buddha who is often interpreted, in texts like the Avatamsaka Sutra, as the dharmakāya of the historical Gautama Buddha. In East Asian Buddhism (Chinese, Korean and Japanese Buddhism), Vairocana is also seen as the embodiment of the Buddhist concept of Śūnyatā. In the conception of the Five Tathagatas of Mahayana and Vajrayana Buddhism, Vairocana is at the centre and is considered a Primordial Buddha.
Now, I, Vairocana Buddha am sitting atop a lotus pedestal; On a thousand flowers surrounding me are a thousand Sakyamuni Buddhas. Each flower supports a hundred million worlds; in each world a Sakyamuni Buddha appears. All are seated beneath a Bodhi-tree, all simultaneously attain Buddhahood. All these innumerable Buddhas have Vairocana as their original body.
He is also mentioned in the Avatamsaka Sutra; however, the doctrine of Vairocana is based largely on the teachings of the Mahavairocana Tantra (also known as the Mahāvairocana-abhisaṃbodhi-tantra) and to a lesser degree the Vajrasekhara Sutra (also known as the Sarvatathāgatatattvasaṃgraha Tantra).
Vairocana is the Primordial Buddha in the Chinese schools of Tiantai and Huayan, also appearing in later schools including the Japanese Kegon, Shingon and esoteric lineages of Tendai. In the case of Shingon and Huayan, Vairocana is the central figure.
In Sino-Japanese Buddhism, Vairocana was gradually superseded as an object of reverence by Amitābha, due in large part to the increasing popularity of Pure Land Buddhism, but Vairocana's legacy still remains in the Tōdai-ji temple with its massive bronze statue and in Shingon Buddhism, which holds a sizeable minority among Japanese Buddhists.
During the initial stages of his mission in Japan, the Catholic missionary Francis Xavier was welcomed by the Shingon monks since he used Dainichi, the Japanese name for Vairocana, to designate the Christian God. As Xavier learned more about the religious nuances of the word, he substituted the term Deusu, which he derived from the Latin and Portuguese Deus. 
The Shingon monk Dohan regarded the two great Buddhas, Amitābha and Vairocana, as one and the same Dharmakāya Buddha and as the true nature at the core of all beings and phenomena. There are several realizations that can accrue to the Shingon practitioner of which Dohan speaks in this connection, as James Sanford points out:
[T]here is the realization that Amida is the Dharmakaya Buddha, Vairocana; then there is the realization that Amida as Vairocana is eternally manifest within this universe of time and space; and finally there is the innermost realization that Amida is the true nature, material and spiritual, of all beings, that he is 'the omnivalent wisdom-body, that he is the unborn, unmanifest, unchanging reality that rests quietly at the core of all phenomena".
Helen Hardacre, writing on the Mahavairocana Tantra, comments that Mahavairocana's virtues are deemed to be immanently universal within all beings: "The principle doctrine of the Dainichikyo is that all the virtues of Dainichi (Mahāvairocana) are inherent in us and in all sentient beings."
With regard to śūnyatā, the massive size and brilliance of Vairocana statues serve as a reminder that all conditioned existence is empty and without a permanent identity, whereas the Dharmakāya is beyond concepts.
The Daibutsu in the Tōdai-ji in Nara, Japan is the largest bronze image of Vairocana in the world. The larger of the Buddhas of Bamiyan in Afghanistan that were destroyed was also a depiction of Vairocana. In Java, Indonesia, the ninth-century Mendut temple near Borobudur in Magelang was dedicated to the Dhyani Buddha Vairocana. Built by the Shailendra dynasty, the temple featured a three-meter tall stone statue of Vairocana, seated and performing the dharmachakra mudrā. The statue is flanked with statues of the bodhisattvas Avalokiteśvara and Vajrapani.