Concept of "gods" in Vajrayana Buddhism

Tenzin Dorje's answer describing "a God in Tibetan Buddhism" seems to me like the notion of Gods in what you call "common original Buddhism", summarized in Wikipedia's Deva (Buddhism) article.

Note that article has a section titled Devas are not gods, which lists ways in which Devas are unlike the "God[s]" of a theistic religion (so in that way it's IMO also true to describe Buddhism as "atheist").

There is some confusion here, in all mainstream forms of Buddhism including Theravada, Mahayana as well as Vajrayana gods are accepted as real. That is they exist and have certain powers.

What they do not have however is unlimited omnipotence as described by the God of Monotheistic religions, because that would break the law of causality.

Most of these gods are like you and me, not enlightened and hence subjected to the same mental afflictions and the cycles of birth and death. The Buddha being enlightened himself is titled the Teacher of Gods and Men. This is why Buddhism/Buddhists are touchy about describing the Buddhas and Bodhisattvas as 'mere' gods, because they are not at the same level of being.

As shown many Buddhists accepted the term 'deity' to describe the Buddha/ Bodhisattvas, even though they are ultimately from the same linguistic origin in meaning as gods in English, because it sounds 'better'.

And yes the Dharma (i.e. the Law, the Truth, the Teachings of the Universe) can be conceptualized as a singular entity, such as the Dharmakaya or the Cosmic Buddha. This might seems to be in contradiction with the concept of denying an Omnipotent God, but the dharma always follow causality and hence no such omnipotence is claimed. In fact causality itself is Dharma.

From Vajrayana view, all phenomena is seen as empty, but with the power to manifest countless Buddha qualities..so perhaps one could say Mahayana is a bit more focused on saying phenomena is empty..and Vajrayana a bit more focused on saying emptiness also manifests pure form unobstructedly.

The Heart Sutra itself says form is emptiness, emptiness is form, emptiness is no different than form, form is no different than emptiness..

By meditating on deities, we remember that all inner and outer phenomena is pure, unobstructed, and appearing only to help sentient beings with compassion..

As i am aware, there is a transcendent entity informally known as the Adi-Buddha but called by various names (Indra/Vajradhara or Vajrasattva, for examples), which could be regarded as a "God" by non-Buddhists, but this would be a gross simplification.

I think it is a very interesting question because you do read about God's in Buddhism. But these God's are different from the western ideas of "God". Infact, I would say "heavenly beings" is much more appropriate to prevent confusion. Buddhist, especially those found in Tibetan Buddhism, believe in the 31 realms of existences as well as the 6-major realms of Samsara. That is:

1. The Realm of Devas (Deva-Gati). This is where the heavenly beings reside.
2. The Realm of Asura (Asura-Gati). This is where the Titans (not like those found in Greek mythologies) reside.
3. The Realm of Hungry Ghosts (Preta-Gati). This is where the ghosts reside (very painful and miserable).
4. The Hell Realm (Naraka-Gati). Where the wicked go for a period of time to be cleansed.
5. The Animal Realm (Tiryagyoni-Gati). Sentient beings are born as animals.
6. The Human Realm (Mausya-Gati). The most desired realm to be reborn as.

Now, the Deva Realm is essentially all about pleasure and excitement. These "heavenly" or "exalted" beings live for a very long time (very being emphasized); but eventually die. They aren't immortal and continue to live in the realms of Samsara. The only men and women who cease to die are the Buddhas. They exist in a realm known as "Buddha Land". Supposedly very beautiful with mountains, rivers, flowers, grass, trees, etc... It is also possible to be born in Buddha land while not being a Buddha yourself. This of course depends on certain circumstances being fulfilled. You're essentially taken under the wings of a Buddha and guaranteed full enlightenment.

The closest to an actual "God" in Buddhism is the leading deva known as Brahma. He was a deity who appeared to Buddha after Shakyamuni became fully enlightened. Some Buddhist may argue that Brahma was the creator and therefore an immortal God; while some maintain he is not. We simply don't know. All we do know is he reigns over Deva-Gati.

Now Buddhist, despite popular belief, may or may not choose to believe in God. It's simply your choice. Therefore, if a Buddhist say's to you, "Buddhist don't believe in a God" that is their personal opinion. It is not the view of every Buddhist. Some Buddhists, especially those who practice in the Western world, do believe in a creator God. The emphasis you find in Buddhism on the disbelief/belief in God really comes down to this quote (which ironically is falsely attributed to Shakyamuni Buddha),

"Do not believe in what you have heard; do not believe in traditions because they have been handed down for many generations; do not believe in anything because it is rumoured and spoken by many; do not believe merely because a written statement of some old sage is produced; do not believe in conjectures; do not believe in that as truth to which you have become attached from habit; do not believe merely the authority of your teachers and elders. After observation and analysis, when it agrees with reason and is conducive to the good and gain of one and all, then accept it and live up to it." (Sayagyi U Ba Khin, 1951)

I hope this clarifies your question.

Extension: a Buddha is said according to the Mahayana tradition to have three bodies (Trikaya)

1. Dharmakaya (Transcendental): Dharmakaya also known as absolute reality is beyond mental comprehensions. It can never manifest itself through form, yet all beings and phenomena originate from it. It is the "true" present moment which pervades everything. Without the Dharmakaya nothing including nothingness could ever exist. It is completely transcendental and is beyond time, form, and the formless. It depends on nothing but itself for existence. Interestingly, the Dharmakaya plays a special role in the origination and unification of the Buddhas. It is through the Dharmakaya that all Buddhas are equally embodiment's of truth.
2. Sambhogakaya (pure body): Sambhogakaya is another appearance which is the manifestation of the Dharmakaya. It is the reward body that Buddhist practitioners receive through practice and the fruits of enlightenment. It is a completely purified body of the Buddhas and occasionally used for appearances to living Bodhisattva's; also, it is the body used to teach men and women in who are in the Pure Lands (Buddha Land). It is through this stage the the Buddhas remain distinct from one another.
3. Nirmanakaya (body): Nirmanakaya is the physical/historical body of a Buddha. For example, Shakyamuni Buddha is the historical person of the Nirmanakaya. His body was subjected to birth, sickness, old age, and eventually death.

It is through the Dharmakaya that the first Buddha, also known as Adi-Buddha, originated from the void as a flame. He has many names and according to some sections of Buddhist traditions they do include Adi-Buddha as God. For example,

"In Indonesia, the term Sanghyang Adi Buddha is agreed upon and used by the Indonesian Supreme Sangha and the Indonesian Buddhist Council as the designation for the God Almighty."

While Buddhists may have different opinions on whether Adi Buddha is God or not; they all agree on his importance and his unique and divine characteristics. It is through the Adi Buddhas incredible mental skills that he manifested (not created) the five Dhyani-Buddhas, the historical Buddhas, and the Bodhisattva's. Some practitioners are even considered to be the physical manifestations of the Adi Buddhas personalities such as Samantabhadra. One of the five Dhyani-Buddhas known as Vairocana is believed to be the Sambhogakaya (pure body) of Shakyamuni; which is the physical extension of the wisdom of Adi Buddha. So is Adi Buddha a God? I'll let you decide.

In Tibetan Buddhism, a God is merely a sentient being that is subject to suffering. Gods have afflictions such as ignorance, anger, attachment and so forth. They have mistaken consciousnesses, and so forth. It is just a type of rebirth. You yourself could be reborn as a God. A god is empty of being permanent, unitary, independent, self-sufficient substantially existent, and according to some schools of Tenets empty of true existence as well, and to others empty of inherent existence as well.

So, 'a god' is just a name referring to a type of being that experiences pleasant feelings for a very long time, before he dies and gets reborn as... maybe a human, or a preta, or a hell being, or an animal or a god again.

There is also the concept of 'deity' but that is another matter that is related to secret mantra and the four bodies of a buddha. Basically, a deity is an emanation or a supreme emanation body which is not a being.