In Hinduism, the Trinity of Gods (the highest form of deities) consists of Brahma (the creator), Vishnu (the preserver), and Shiva (the destroyer). Each of these deities represent an aspect of cosmic forces that shape our reality.
But this reality extends beyond the space-time we perceive through our senses, in the form of differnt worlds. Since thousands of years, incredible meditators (Sadhus) have documented the perception of these worlds. Though Vishnu resides in a higher world, he descends down to our plane once in a few thousand years, in the form of an reincarnation (avatara).
About 5,000 years ago, it was in his eighth reincarnation, that Vishnu appeared as ‘Krishna’. Krishna is the central figure in the prominent Hindu text Bhagavad Geeta (the divine song), a book about the four paths to enlightenment: Karma Yoga (the path of action and serive), Bhakti Yoga (the path of devotion), Raja Yoga (the path of meditation), and Jnana Yoga (the path of intellect).
And the birth of Krishna is celebrated as what is known as the festival of Janmashtami in Hinduism.