Tathāgata (Devanagari तथागत) - Chinese 如来, Rú lái), Japanese Nyorai (如来? ), Korean Yeorae (여래), Vietnamese Như Lai, Tibetan de-bZhin-gShegs-pa-it is a Sanskrit and Pāli word that can be translated as "He who thus comes" or "He who thus goes";this ambiguity is generally interpreted as intentional and the term is translated as "he who comes and goes in the same way (as all Buddhas)."
In fact, Tathāgata is the name by which the "historical Buddha" Śākyamuni (Siddhartha Gautama) refers to himself in his sermon collections (the Āgama-Nikāya), and in the same way he is referred to by his interlocutors, to highlight the rare and indefinite ontological state of a fully enlightened being who is beyond existence and non-existence, in fact beyond any state expressible by words.
In the Mahāyāna sutras it also indicates other buddhas.
Thus come / Thus gone
The term Tathāgata can be read as tathā-gata or as Tathā-āgata, where the former means "so gone" while the latter means "so come."
This difference represents an important dichotomy in the Buddhist tradition: Tathāgata as "so gone" implies that a Buddha is a pioneer and that the task of the worshipper is to follow him and draw inspiration and guidance from him, eventually arriving by attaining the same state of knowledge and liberation;
Tathāgata as "so come" (this version translated by the Chinese Rú lái and the Japanese Nyorai), on the other hand, implies that a Buddha comes to save sentient beings and offer them refuge, and what is required of the worshipper is prayer and devotion.
Among the various schools, Amidism follows the second approach; most schools, however, adopt a hybrid of the two approaches.
The Buddha was often asked whether the Tathāgata still exists after death or not. To this question he replied that the Tathāgata could not be identified in life, much less could it be once he died.
Furthermore, neither can the group of the five constituents of existence be considered the Tathāgata, nor can the Tathāgata be found outside of these bodily and mental phenomena.
That is to say, there are yes bodily and mental phenomena, but they are changing and impermanent phenomena, ephemeral and devoid of self. In this sense the Tathāgata has "thus gone [beyond]": through the wisdom and knowledge attained by penetrating the innermost nature of existing he has gone beyond the apparent, corporeality and conceptuality of being.