Before the Smurfs, the Blue Man Group, or the cat-people from Avatar, there was Krishna.
Discussion of this deity is a little difficult due to the fact that different varieties of Hinduism see him in different ways. His original portrayal was as the eighth avatar of the god Vishnu, but later Krishnaism made him into the supreme being. I don’t think there’s any official word on why Krishna is usually depicted as having blue skin, but one possible derivation for his name is “the dark one,” and the skin color and name might show a connection to the Dravidian people of southern India.
As with many divine heroes, Krishna’s birth was prophesied, and someone tried to prevent it. In this case, the nasty Kamsa, son of a demon and King of Mathura, was told that he would be killed by his nephew. Therefore, when his sister Devaki began giving birth, he would kill her children. She managed to save her eighth born, Krishna, by exchanging him with the daughter of the cowherd Nanda and his wife Yashoda.
The daughter turned out to be the incarnation of the goddess Maya, and she flew away and taunted Kamsa when he tried to kill her. So Krishna ended up being raised by Nanda and Yashoda. In his youth, he was a notorious prankster and thief, and seduced milkmaids by playing his flute.
There was supposedly some moral lesson in this, but I also think Krishna wanted to be the fun avatar. I mean, how many milkmaids did Jesus seduce?
While still pretty young, he killed Kamsa and all the assassins the half-demon king sent after him, and became a prince under Kamsa’s father. Later in life, he fought with the Pandavas against the Kauravas, and dictated what would become known as the Bhagavad Gita to the Pandavas’ heroic leader Arjuna.
Basically, the point Krishna made to Arjuna was that he had to do his duty, and that death on the battlefield was merely temporary, as the soul was immortal. I have to say I’ve heard better morals. How did the same guy go from orgies with milkmaids to promoting warfare? That’s part of the oddity of Hinduism, at least as I see it. It’s very liberal in terms of what you can believe and how you can worship, yet incredibly rigid in social conventions and structure. Anyway, Krishna’s traditional lifetime is said to have been from 3228 through 3102 BC, after which he ascended into heaven. Or, depending on whom you ask, he might have died from an arrow in his foot. Regardless, his disappearance from the earthly realm marked the beginning of the Kali Yuga, the last and most corrupt of the four ages.
Worship of Krishna is generally part of bhakti yoga, in which devotion to God (i.e., Krishna himself) is the most important part. Devotees shouldn’t neglect the material world, but it’s really Krishna who’s important. Krishnaism has spread by means of the International Society of Krishna Consciousness, better known as the Hare Krishna movement after its mantra.