I dub this entity the epitome of all that is confusing, complex, and contradictory in Hinduism!
It's Vedic, it isn't Vedic, it's considered to be an avatar of Vishnu - no, it's actually Krishna - no, it's connected to Shiva - no, it's connected to Buddha - no, it's actually tribal and connected to tree worship. It has no mythology - no, here are the myths connected to it.
Balabhadra, Subhadra and Jagannatha. Kalighat, Calcutta, 1860. The Jagannath trio, consisting of Jagannatha painted black as an alternative form of Krishna, Lord of the Universe, in the company of his brother Balabhadra and their little sister Subhadra in the middle.
One just has to scroll/scan through the headers in the article to glean all the disagreement:
https://en.wikipedia.org/wiki/Jagannath