The earliest known Buddhist Tantra is possibly the Mahavairocana Tantra, which has been mentioned and collected by the Chinese pilgrim Wu-Xing c. 680 CE.
Some of the content in the Yoga Upanishads is similar to Buddhist Tantric traditions. They were influenced by Hindu and Buddhist ideas, as well as different types of gods and goddesses.
Some Tantras contain practices that people find to be bad. For example, some people drink alcohol and other forbidden substances. And some Tantras include sexual rituals.
In the Buddhist Tantras, there are some interesting ideas, which may seem novel to proponents of other spiritual beliefs! One is that... you can be happy even when you have a body. Another idea is that women and female deities are also important. There are also ideas about negative feelings, where they can be utilized to bring about deep inner transformation. These negative thoughts and feelings can be useful for people who want to be free from suffering. This concept is best expressed by this quote from the Hevajra Tantra, which states that "the world is bound by passion, also by passion it is released".
Buddhist Tantra quickly spread out of India into nearby countries like Tibet and Nepal in the eighth century, as well as to many other regions in Southeast Asia.
Buddhist Tantra arrived in China during the Tang Dynasty, where it was known as Tangmi and was brought to Japan by Kukai where it is known as Shingon. To this day, it remains the main Buddhist tradition in Nepal, Mongolia and Tibet- where it is known as Vajrayana.